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diff --git a/old/60937-0.txt b/old/60937-0.txt deleted file mode 100644 index 86edc20..0000000 --- a/old/60937-0.txt +++ /dev/null @@ -1,10575 +0,0 @@ -The Project Gutenberg EBook of The Philosophy of Health; Vol 2, by -Thomas Southwood-Smith - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: The Philosophy of Health; Vol 2 - or, an exposition of the physical and mental constitution of man.... - -Author: Thomas Southwood-Smith - -Release Date: December 16, 2019 [EBook #60937] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE PHILOSOPHY OF HEALTH; VOL 2 *** - - - - -Produced by Chris Curnow, Les Galloway and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - - - - - THE - - PHILOSOPHY OF HEALTH; - - OR, - - AN EXPOSITION - - OF THE - - PHYSICAL AND MENTAL CONSTITUTION - OF MAN, - - WITH A VIEW TO THE PROMOTION OF - - HUMAN LONGEVITY AND HAPPINESS. - - BY - - SOUTHWOOD SMITH, M.D., - _Physician to the London Fever Hospital, to the Eastern Dispensary, - and to the Jews’ Hospital_. - - IN TWO VOLUMES. VOL. II. - - _THIRD EDITION._ - - LONDON: - - C. COX, 12, KING WILLIAM STREET, STRAND. - - 1847. - - - London: Printed by WILLIAM CLOWES and SONS, Stamford Street. - - - - - CONTENTS OF VOL. II. - - - CHAPTER VIII. - - OF THE FUNCTION OF RESPIRATION. - - Respiration in the plant; in the animal—Aquatic and aërial - respiration—Apparatus of each traced through the lower to the - higher classes of animals—Apparatus in man—Trachea, Bronchi, Air - Vesicles—Pulmonary artery—Lungs—Respiratory motions: inspiration; - expiration—How in the former air and blood flow to the lungs; how - in the latter air and blood flow from the lungs—Relation between - respiration and circulation—Quantity of air and blood employed in each - respiratory action—Calculations founded on these estimates—Changes - produced by animal respiration on the air: changes produced by - vegetable respiration on the air—Changes produced by respiration on - the blood—Respiratory function of the liver—Uses of respiration Page 1 - - - CHAPTER IX. - - OF THE FUNCTION OF GENERATING HEAT. - - Of the temperature of living bodies—Temperature of plants—Power - of plants to resist cold and endure heat—Power of generating - heat—Temperature of animals—Warm-blooded and cold-blooded - animals—Temperature of the higher animals—Temperature of the different - parts of the animal body—Temperature of the human body—Power of - maintaining that temperature at a fixed point, whether in intense - cold or intense heat—Experiments which prove that this power is a - vital power— Evidence that the power of generating heat is connected - with the function of respiration—Analogy between respiration and - combustion—Phenomena connected with the functions of the animal body, - which prove that its power of generating heat is proportionate to - the extent of its respiration—Theory of the production of animal - heat—Influence of the nervous system in maintaining and regulating the - process—Means by which cold is generated, and the temperature of the - body kept at its own natural standard during exposure to an elevated - temperature Page 120 - - - CHAPTER X. - - OF THE FUNCTION OF DIGESTION. - - Process of assimilation in the plant; in the animal—Digestive - apparatus in the lower classes of animals; in the higher - classes; in man—Digestive processes—Prehension, Mastication, - Insalivation, Deglutition, Chymification, Chylification, Absorption, - Fecation—Structure and action of the organs by which these operations - are performed—Ultimate results—Powers by which those results are - accomplished—Two kinds of digestion, a lower and a higher; the former - preparatory to the latter Page 159 - - - CHAPTER XI. - - OF THE FUNCTION OF SECRETION. - - Nature of the function—Why involved in obscurity—Basis of the - apparatus consists of membrane—Arrangement of membrane into elementary - secreting bodies—Cryptæ, follicles, cæca, and tubuli—Primary - combinations of elementary bodies to form compound organs—Relation of - the primary secreting organs to the blood-vessels and nerves—Glands, - simple and compound—Their structure and office—Development of glands - from their simplest form in the lowest animals to their most complex - form in the highest animals—Development in the embryo—Number and - distribution of the secreting organs—How secreting organs act upon - the blood—Degree in which the products of secretion agree with, and - differ from, the blood—Modes in which modifications of the secreting - apparatus influence the products of secretion—Vital agent by which the - function is controlled—Physical agent by which it is effected Page 279 - - - CHAPTER XII. - - OF THE FUNCTION OF ABSORPTION. - - Evidence of the process in the plant, in the animal—Apparatus - general and special—Experiments which prove the absorbing power of - blood-vessels and membrane—Decomposing and analysing properties - of membrane—Endosmose and exosmose—Absorbing surfaces, pulmonary, - digestive, and cutaneous—Lacteal and lymphatic vessels—Absorbent - glands—Motion of the fluid in the special absorbent vessels—Discovery - of the lacteals and lymphatics—Specific office performed by the - several parts of the apparatus of absorption—Condition of the system - on which the activity of the process depends—Uses of the function - Page 332 - - - CHAPTER XIII. - - OF THE FUNCTION OF EXCRETION. - - In what excretion differs from secretion—Excretion in the - plant—Quantity excreted by the plant compared with that excreted - by the animal—Organs of excretion in the human body—Organization - of the skin—Excretory processes performed by it—Excretory - processes of the lungs—Analogous processes of the liver—Use of the - deposition of fat—Function of the kidneys—Function of the large - intestines—Compensating and vicarious actions—Reasons why excretory - processes are necessary—Adjustments Page 369 - - - CHAPTER XIV. - - OF THE FUNCTION OF NUTRITION. - - Composition of the blood—Liquor sanguinis—Recent account of the - structure of the red particles—Formation of the red particles in - the incubated egg—Primary motion of the blood—Vivifying influence - of the red particles—Influence of arterial and venous blood on - animal and organic life—Formation of human blood—Course of the new - constituents of the blood to the lungs—Space of time required for the - complete conversion of chyle into blood after its first transmission - through the lungs—Distribution of blood to the capillaries when - duly concentrated and purified—Changes wrought upon the blood while - it is traversing the capillaries—Evidence of an interchange of - particles between the blood and the tissues—Phenomena attending the - interchange—Nutrition, what, and how distinguished from digestion—How - the constituents of the blood escape from the circulation—Designation - of the general power to which vital phenomena are referrible—Conjoint - influence of the capillaries and absorbents in building up - structure—Influence of the organic nerves on the process—Physical - agent by which the organic nerves operate—Conclusion Page 422 - - - - - THE - - PHILOSOPHY OF HEALTH. - - - - - CHAPTER VIII. - - OF RESPIRATION. - - Respiration in the plant; in the animal—Aquatic and aërial - respiration—Apparatus of each traced through the lower to the - higher classes of animals—Apparatus in man—Trachea, Bronchi, Air - Vesicles—Pulmonary artery—Lung—Respiratory motions: inspiration; - expiration—How in the former air and blood flow to the lung; how - in the latter air and blood flow from the lung—Relation between - respiration and circulation—Quantity of air and blood employed in each - respiratory action—Calculations founded on these estimates—Changes - produced by animal respiration on the air: changes produced by - vegetable respiration on the air—Changes produced by respiration on - the blood—Respiratory function of the liver—Uses of respiration. - - -313. No organized being can live without food and no food can nourish -without air. In all creatures the necessity for air is more urgent than -that for food, for some can live days, and even weeks, without a fresh -supply of food, but none without a constant renewal of the air. - -314. The food having undergone the requisite preparation in the -apparatus provided for its assimilation, is brought into contact with -the air, from which it abstracts certain principles, and to which -it gives others in return. By this interchange of principles the -composition of the food is changed: it acquires the qualities necessary -for its combination with the living body. The process by which the air -is brought into contact with the food, and by which the food receives -from the air the qualities which fit it for becoming a constituent part -of the living body, constitutes the function of respiration. - -315. In the plant, the air and the food meet in contact and re-act -on each other in the leaf. The crude food of the plant having in its -ascent from the root through the stalk, received successive additions -of organic substances, by which its nature is assimilated to the -chemical condition of the proper nutritive fluid of the plant (320 -and 325), undergoes in the leaf a double process; that of Digestion -and that of Respiration. The upper surface of the leaf is a digestive -apparatus, analogous to the stomach of the animal; the under surface -of the leaf is a respiratory apparatus, analogous to the lung of the -animal. For the performance of this double function, incessantly -carried on by the leaf, its organization is admirably adapted. - -[Illustration: Fig. CXXII. - - View of the net-work which forms the solid structure of the leaf, and - which consists partly of woody fibres, and partly of spiral vessels. - 1. Vessels of the upper surface; 2. vessels of the under surface; 3. - distribution of the vessels through the substance of the leaf; 4. - interspaces between the vessels occupied by parenchyma or cellular - tissue.] - -316. The solid skeleton of the leaf consists of a net-work composed -partly of woody fibres and partly of spiral vessels which proceed -from the stem, and which are called veins (fig. CXXII. 1, 3). In -the interstices between the veins is disposed a quantity of cellular -tissue, termed the parenchyma of the leaf (fig. CXXII. 4): the whole is -enveloped in a membrane, called the cuticle (fig. CXXIII. 1), which is -furnished with apertures denominated stomata, or stomates (fig. CXXIV.). - -[Illustration: Fig. CXXIII. - - Vertical section of the leaf as it appears when seen highly magnified - under the microscope. 1. Cells of the cuticle filled with air; 2. - double series of cylindrical cells occupying the upper surface of - the leaf filled with organic particles; 3. irregular cells forming - a reticulated texture occupying the under surface of the leaf; 4. - interspaces between the cells, termed the intercellular passages or - air chambers.] - -317. The cuticle consists of a layer of minute cellules, colourless, -transparent, without vessels, without organic particles of any kind, -and probably filled with air (fig. CXXIII. 1). These cellules open -externally, at certain portions of the cuticle, by apertures or -passages which constitute the stomates (fig. CXXIV.), and which present -the appearance of areolæ with a slit in the centre (fig. CXXIV.). -They form a kind of oval sphincters, which are capable of opening -or shutting, according to circumstances, and they are disposed on -both surfaces of the leaf, but most abundantly on the under surface, -excepting in leaves which float on water, in which they are always on -the upper surface only. - -[Illustration: Fig. CXXIV. - - View of the stomata of a leaf, some of them represented as open and - others as closed.] - -318. The cellular tissue or parenchyma, immediately beneath the -cuticle, when examined in thin slices, and viewed under a microscope -with a high magnifying power, presents a regular structure disposed -in perfect order. It consists, on the upper surface, of a layer, and -sometimes of two and even three layers, of vesicles of an oblong or -cylindrical form, placed perpendicularly to the surface of the leaf, -set close to each other (fig. CXXIII. 2), and filled with organic -particles constituting the green matter which determines the colour -of the leaf. On the under surface, on the contrary, the vesicles, -which are larger than the cylindrical, are of an irregular figure, -and are placed in an horizontal direction, at such distances as to -leave wide intervals between each other (fig. CXXIII. 3); yet uniting -and anastomosing together, and thus forming a reticulated tissue, -presenting the appearance of a net with large meshes (fig. CXXIII. 3). - -319. A leaf, then, consists of a double congeries of vesicles -containing organic particles, penetrated by woody fibre and air vessels -(which is probably the true nature of the spiral vessels), the whole -being enclosed within a hollow stratum of air-cells. - -320. The crude sap, composed principally of water, holding in solution -carbonic acid, acetic acid, sugar, and a matter analogous to gum, -is transmitted through the leaf-stalk to the cylindrical vesicles -of the upper surface of the leaf (fig. CXXIII. 2). These vesicles -exhale a large proportion of the water; the evaporation of which is -so powerfully assisted by the action of the sun’s rays, that it would -probably become excessive, were it not for the perpendicular direction -of the cylindrical vesicles (fig. CXXIII. 2); but in consequence of -their being disposed perpendicularly to the surface of the leaf, their -ends only are presented towards the heavens (fig. CXXIII. 2), and thus -the main part of their surface is protected from the direct influence -of the solar rays. The primary effect of the evaporation carried on in -the cylindrical vesicles, is the condensation of the organic matters -contained in the sap. - -321. At the same time that the cylindrical vesicles pour the -superfluous water of the sap into the surrounding atmosphere, they -abstract from the atmosphere in return carbonic acid, which, together -with that already contained in the sap, is decomposed. The oxygen is -evolved; the carbon is retained. The physical agent by which this -chemical change, which constitutes the digestive process of the plant, -is effected, is the solar ray; hence the vesicles which contain the -fluid to be decomposed, are placed on the upper surface of the leaf, -where their contents are fully exposed to the action of the sun; -and hence also this process takes place only during the day, and -most powerfully under the direct solar ray: but although the direct -influence of the sun be highly conducive to the process, yet it is -not indispensable to it; for it goes on in daylight although there be -no sunshine. Light, then, would appear to be the physical agent which -effects on the crude food of the plant a change analogous to that -produced on the crude food of the animal by the juices of the stomach. - -322. After the sap has been elaborated in the cylindrical vesicles, -by the exhalation of its watery particles, by the condensation of its -organic matter, by the retention of carbon and the evolution of oxygen, -it is transmitted to the reticulated vesicles of the under surface of -the leaf (fig. CXXIII. 3), These vesicles, large, loose, and expanded, -as they have an opposite function to perform, are arranged in a mode -the very reverse of the cylindrical: in such a manner as to present -the greatest possible extent of surface to the surrounding air (fig. -CXXIII. 3): at the same time the broad interspaces between them (fig. -CXXIII. 4) are so many cavernous air-chambers into which the air is -admitted through the stomates (fig. CXXIV.). The cylindrical vesicles, -exposed to the direct rays of the sun, are protected by the closeness -with which they are packed; and by the small extent of surface they -present to the heavens: the reticulated vesicles, whose function -requires that they should have the freest possible exposure to the -surrounding air, are protected from the solar ray, first by their -position on the under surface of the leaf; and, secondly, by the dense -and thick barrier formed by the stratum of cylindrical vesicles (fig. -CXXIII. 2). - -323. In the cylindrical vesicles carbonic acid is decomposed; in the -reticulated vesicles, on the contrary, carbonic acid is re-formed. The -oxygen required for this generation of carbonic acid is abstracted -partly from the surrounding air; the carbon is derived partly, -perhaps, from the air, but chiefly from the digested sap, and the -carbonic acid, formed by the union of these elements, is evolved into -the surrounding atmosphere. - -324. This operation, which is strictly analogous to that of respiration -in the animal, in which carbonic acid is always generated and expired, -is carried on chiefly in the night. In this manner, under the influence -of the solar light, the leaf decomposes carbonic acid; retains the -carbon and returns the greater part of the oxygen to the air in a -gaseous form. At night, in the absence of the solar ray, the leaf -absorbs oxygen, combines this oxygen with the materials of the sap to -produce carbonic acid, which, as soon as formed, is evolved into the -surrounding air. The carbonic acid gas exhaled during the night is -re-absorbed during the day and oxygen is evolved; and this alternate -action goes on without ceasing; whence the plant deteriorates the -air by night, by the abstraction of its oxygen and the exhalation of -carbonic acid; and purifies it by day by the evolution of oxygen and -the abstraction of carbonic acid. - -325. The result of these chemical actions is the conversion of -the crude sap into the proper nutritive juice of the plant. When -it reaches the cylindrical vesicles, the sap is colourless, not -coagulable, without globules, composed chiefly of water holding in -solution carbonic and acetic acids, sugar, gum, and several salts; -when it leaves the reticulated vesicles it is a greenish fluid, -partly coagulable and abounding with organic particles under the -form of globules. Its chemical composition is now wholly changed; it -consists of resinous matter, starch, gluten, and vegetable albumen. It -is now thoroughly elaborated nutritive fluid; the proper food of the -plant (cambium); rich in all the principles which are fitted to form -vegetable secretions: it is to the plant what arterial blood is to -the animal, and like the vital fluid formed in the lung, the cambium -elaborated in the leaf, is transmitted to the different parts and -organs of the plant to serve for their nutrition and development. - -326. The formation of this nutritive fluid by the plant is a vital -process, as necessary to the continuance of its existence, as the -process of sanguification is necessary to the maintenance of the life -of the animal. If the plant be deprived of its leaves, if the cold -destroy, or the insect devour them, the nutrition of the plant is -arrested; the development of the flowers, the maturation of the fruit, -the fecundation of the seeds, all are stopped at once, and the plant -itself perishes. - -327. The proper nutritive juice of the plant, completed by the process -of respiration, is formed by the elaboration of organic combinations -of a higher nature than those afforded by the sap. Acid, sugar, gum -(325) are converted into the higher organic compounds, resin, gluten, -starch, albumen, probably by chemical processes, the result of which -is the inversion of the relative proportions of oxygen and carbon. In -the organic matters contained in the sap, the proportion of oxygen, -compared with that of carbon, is in excess; on the contrary, in the -higher compounds contained in the cambium, the carbon preponderates: by -the inversion of the relative proportions of these two elements, the -organic compounds of a lower nature, appear to be changed into those of -a higher; to be brought into a chemical condition nearer to that of the -proper substance of the plant; a condition in which they receive the -last degree of elaboration preparatory to their conversion into that -substance. - -328. In the process of respiration in the animal, as in the plant, -parts of the digested aliment mix with the air; parts of the air mix -with the digested aliment; and by this interchange of principles, the -chemical composition of the aliment acquires the closest affinity to -that of the animal body; is rendered fit to combine with it; fit to -become a constituent part of it. - -329. The extent and complexity of the respiratory apparatus in the -animal, is in the direct ratio of the elevation of its structure and -the activity of its function, to which the quantity of air consumed by -it is always strictly proportionate. - -330. The process of respiration in the animal is effected by two -media, air and water; but the only real agent is the air; for the -water contributes to the function only by the air contained in it. -Respiration by water is termed aquatic, that by the atmosphere, -atmospheric or aërial respiration. - -331. The quantity of air contained in water being small, aquatic -is proportionally less energetic than aërial respiration; and, -accordingly, the creatures placed at the bottom of the animal scale, -having the simplest structure and the narrowest range of function, are -all aquatic. - -332. Whatever the medium breathed, respiration in the animal is -energetic in proportion to the extent of the respiratory surface -exposed to the surrounding element. As the water-breathing animals -successively rise in organization, their respiratory surface becomes -more and more extended, and a proportionally larger quantity of water -is made to flow over it. It is the same in aërial respiration: the -higher the animal, the greater the extent of its respiratory surface; -and the larger the bulk of air that acts upon it. - -333. Whatever the medium breathed, respiration is effected by the -contact of fresh strata of the surrounding element with the respiratory -surface. The mode in which this constant renewal of the strata is -effected, is either by the motion of the body to and fro in the -element; or by the creation of currents in it, which flow to the -respiratory surface. A main part of the apparatus of respiration -consists of the expedients necessary to accomplish these two objects; -and that apparatus is simple, or complex, chiefly according to the -extent of the mechanism requisite to effect them. - -334. Whatever the medium breathed, the organic tissue which constitutes -the essential part of the immediate organ of respiration is the skin. -The primary tissue of which the skin is composed is the cellular (23 -et seq.), which, organized into mucous membrane (33 et seq.), forms -the essential constituent of the skin (34). In all animals the skin -covers both the external and the internal surfaces of the body (34). -When forming the external envelop, this organ commonly retains the -name of skin; when forming the internal lining, it is generally called -mucous membrane; and in all animals, from the monad to man, either in -the form of an external envelop, or an internal lining, or by both in -conjunction, or by some localization and modification of both, the -skin constitutes the immediate organ of respiration. In different -classes of animals it is variously arranged, assumes various forms, -and is placed in various situations, according to the medium breathed, -and the facility of bringing its entire surface into contact with the -surrounding element; but in all, the organ and its office are the -same: it is the modification only—that modification being invariably -and strictly adaptation, which constitutes the whole diversity of the -immediate organ of respiration. - -335. At the commencement of the animal scale, in the countless tribes -of the polygastrica (vol. i. p. 34, et seq.), respiration is effected -through the delicate membrane which envelops the soft substance of -which their body is composed. The air contained in the water in which -they live, penetrating the porous external envelop, permeates every -part of their body; aërates their nutritive juices; and converts them -immediately into the very substance of their body. They are not yet -covered with solid shells, nor with dense impervious scales, nor with -any hard material which would exclude the general respiratory influence -of water, or render necessary any special expedient to bring their -respiratory surface into contact with the element. - -336. But in some tribes even of these simple creatures there is visible -by the microscope an afflux of their nutritive juices to the delicate -pellicle that envelops them, in the form of a vascular net-work, in -which there appears to be a motion of fluids, probably the nutritive -juices flowing in the only position of the body in which they could -come into direct contact with the surrounding element. In some more -highly advanced tribes, as in wheel animalcules, there is an obvious -circulating system in vessels near the surface of the skin. In other -tribes, the internal surface constituting the alimentary canal, is of -great extent and width, and forms numerous cavities which are often -distended with water. In this manner a portion of the internal, as -well as the external surface is made contributary to the function -of respiration, and this extended respiration is conducive to their -great and continued activity, to their rapid development, and to the -extraordinary fertility of their races. - -[Illustration: Fig. CXXV.—_Medusa._ - - 1. The mouth; 2. the stomach; 3. large canals going from the stomach; - 4. smaller canals which form; 5. a plexus of vessels at the margin of - the disc serving for respiration; 6. margin of the disc.] - -337. In creatures somewhat higher in the scale, a portion of the -external surface is reflected inwards in the form of a sac, with an -external opening (fig. CXXV. 1). In some medusæ there are numerous -sacs of this kind, which pass inwards until they are separated only -by thin septa from the cavities of the stomach. The water permeating -and filling these sacs comes into contact with an interior portion -of the body, not to be reached through the external surface. At the -margin of the disk (fig. CXXV. 6) there is spread out a delicate -net-work of vessels (fig. CXXV. 5); these vessels communicate with -small canals (fig. CXXV. 4) which open into larger canals (fig. CXXV. -3) that proceed directly from the stomach (fig. CXXV. 2). As the -aliment is prepared by the stomach, it is transmitted thence by these -communicating canals to the exterior net-work of vessels where it is -aërated. - -338. As organization advances, as the component tissues of the body -become more dense, and are moulded into more complex structures, when, -moreover, these structures are placed deep in the interior of the body, -far from the external envelop, and proportionally distant from the -surrounding element, the respiratory apparatus necessarily increases -in complexity. The first complication consists in the formation of -minute, delicate, transparent tubes (fig. CXXVI. 5), which communicate -with the external surface by a special organ (fig. CXXVI. 4) that -conveys water into the interior of the body (fig. CXXVI. 5). By means -of these ramifying water-tubes, upon the delicate walls of which the -blood-vessels are spread out in minute and beautiful capillaries, the -water is brought into immediate contact with the vascular system. - -[Illustration: Fig. CXXVI.—_Holothuria._ - - 1. Mouth; 2. salivary sacs; 3. intestine; 4. cloaca; 5. ramified - tubes, conveying water for respiration into the interior of the body.] - -339. Next, in the ascending scale, the external envelop of the body is -extended into a distinct additional or supplemental organ, by which -the function of the skin is assisted. This additional organ is called -branchia or gill. The simplest form of branchia consists of folds -or duplicatures of skin, forming ramified tufts (fig. CXXVII. 1), -which in general have a regular and often a symmetrical disposition -on the external surface (fig. CXXVII. 1). Sometimes, as in the water -breathing annelides, these tufts form a fan-like expansion around the -head; but at other times they are disposed in regular series along the -whole extent of the body. - -[Illustration: Fig. CXXVII.—_Lumbricus Marinus._ - - 1. Respiratory tufts. 2. Artery and vein, supplying the respiratory - apparatus. 3. Dorsal vessel.] - -340. Instead of branchiæ in the form of ramified tufts, the ascending -series of animals, namely, the higher crustacea, possess branchiæ -composed of numerous, delicate, thin laminæ or leaves, divided from -each other, yet placed in close proximity, like the teeth of a -fine comb, whence this arrangement is termed pectinated. Over the -blood-vessels of the system spread out on these delicate, fringed, -pectinated leaves, the water is driven in constant streams. - -341. Still higher in the scale, as in molluscous animals, an internal -sac is formed to which are sometimes attached numerous tufts; but which -at other times is itself plaited into beautifully disposed regular -folds, crowded with blood-vessels and constantly bathed with fresh -currents of water. - -[Illustration: Fig. CXXVIII. - - Trichoda showing the form and a frequent arrangement of Cilia.] - -342. In all these water-breathing creatures, respiration is effected, -either by the progressive motion of the body through the water, or by -the creation of currents which bring fresh strata of the fluid into -contact with the respiratory surfaces. Both objects are effected by the -same instruments, namely, minute fibres having the appearance of fine -hairs or bristles. These fibres which are called cilia, have in general -an elongated, flattened, thin, and tapering form (fig. CXXVIII). Their -number, position, and arrangement, are infinitely various. Sometimes, -as in the poriferous animals, they are so minute that they cannot -be rendered visible to the eye even by the microscope, although the -evidence of their existence and action is indubitable. Sometimes they -are of great size and strength, attached by distinct ligaments to the -body and moved by powerful muscles, as in wheel animalcules. Sometimes, -as in polypiferous animals, they are disposed around the orifice of the -polypes or upon the sides of the tentacula, the instruments by which -the animal seizes its prey. Sometimes they are symmetrically disposed -in longitudinal series along the surface of the body, as in the Beroe -pileus; at other times they are arranged in circles; whenever there -are branchiæ, they are disposed around the margin of the branchial -apertures, and always on the margins of the minute meshes which compose -the branchiæ themselves. - -343. In some cases the number of these cilia is immense. Each polype, -for example, has usually twenty-two tentacula, and there are about -fifty cilia on each side of a tentaculum, making two thousand two -hundred cilia on each polype. As there are about one thousand eight -hundred cells in each square inch of surface, and the branches of an -ordinary specimen present about ten square inches of surface, we may -estimate that an ordinary specimen of this zoophite presents more -than eighteen thousand polypes, three hundred and ninety-six thousand -tentacula, and thirty-nine million six hundred thousand cilia. But -other species contain more than ten times these numbers. Dr. Grant has -calculated that there are about four hundred million cilia on a single -Flustra foliacea. - -344. The motions of these cilia are regular, incessant, and when in -full activity far too rapid to be distinguished by the eye even when -assisted by the microscope. They are generally to be perceived only -when their motions are comparatively feeble. They produce two effects. -In animals capable of progressive motion, they transport the body -through the water, while they constantly bring new strata of water into -contact with the respiratory surface. In this case they are partly -organs of locomotion, and partly organs subservient to respiration. -On the other hand, in animals which are not capable of moving from -place to place, they create currents by which the respiratory surface -is constantly bathed with fresh streams of water. These currents -are regular, constant, unceasing. Like some physical phenomena not -depending on vitality, it is a continued stream as regular as the -motions of rivers from their source to the ocean, or any other -movements depending on the established order of things. Dr. Grant, to -whom we are indebted for our knowledge of the true nature of these -currents, as well as of the instruments by which they are effected, -gives the following account of the observation which led to the -discovery:—“I put,” says he, “a small branch of the spongia coalita, -with some sea water into a watch-glass, under the microscope, and on -reflecting the light of a candle through the fluid, I soon perceived -that there was some intestine motion in the opaque particles floating -through the water. On moving the watch-glass, so as to bring one of the -apertures on the side of the sponge fully into view, I beheld, for the -first time, the splendid spectacle of this living fountain, vomiting -forth from a circular cavity an impetuous torrent of liquid matter, -and hurling along in rapid succession opaque masses which it strewed -everywhere around. The beauty and novelty of such a scene in the animal -kingdom long arrested my attention, but after twenty-five minutes of -constant observation, I was obliged to withdraw my eye from fatigue, -without having seen the torrent for one instant change its direction, -or diminish in the slightest degree the rapidity of its course. I -continued to watch the same orifice, at short intervals, for five -hours, sometimes observing it for a quarter of an hour at a time, but -still the stream rolled on with a constant and equal velocity.” - -[Illustration: Fig. CXXIX.—_Diagram of the Apparatus of the Circulation -and Respiration in the Fish._ - 1. Auricle (Single) of the heart. 2. Ventricle (single) of the heart. - 3. Trunk of the branchial artery. 4. Division of the branchial - artery going to the branchiæ or gills. 5. Leaves of the branchiæ. 6. - Branchial veins, which return the blood from the branchiæ, and unite - to form. 7. the aorta, by the division of which the aërated blood is - carried out to the system.] - -345. The simple expedients which have been described suffice for -carrying on the function of respiration in the water-breathing -invertebrata; but in creatures that possess a vertebral column, and the -more perfect skeleton of which it forms a part, there is a prodigious -advancement in the organization of the whole body, of the nervous and -muscular systems especially, the organs of the animal, as well as in -all the organs of the organic life. A corresponding development of -the function of respiration is indispensable. Accordingly, a sudden -and great development in the apparatus of this function is strikingly -apparent in fishes, the lowest order of the vertebrata, in which the -branchiæ, though still preserving the same form as in the animals -below them, are large and complex organs. The branchiæ of fishes -still consist of fringed folds of membrane disposed, as in the -preceding classes, in laminæ or leaves (fig. CXXIX. 5); but there are -now commonly four series of these leaves, on each side of the body, -placed in close approximation to each other, the several leaves being -divided into minute fibres, which are set close like the barbs of a -feather, or the teeth of a fine comb (fig. CXXIX. 5). Each leaf rests -either on a cartilaginous or a bony arch, which exactly resembles the -rib of the more perfect skeleton, and performs a strictly analogous -function; for these arches are capable of alternately separating from, -and of approximating to, each other, and these alternate motions are -effected by appropriate muscles. As these movements of separation or -approximation take place, the branchiæ are either opened or closed, -and their surface proportionally expanded or contracted. Upon these -leaves (fig. CXXIX. 5) the veins (347) of the system (fig. CXXIX. 4) -are spread out in a state of capillary division of extreme minuteness, -forming a net-work of vessels of extreme tenuity and delicacy. So -prodigiously is the surface increased for the expansion of these -vessels by the leaf-like disposition of the branchiæ, that it is -computed that the branchial surface of the skate is at least equal to -the surface of the whole human body. - -346. Through this extended surface the whole blood of the system -must circulate, and every point of it must be unceasingly bathed -with fresh streams of water. To generate the force necessary for -the accomplishment of these objects, an increase of power must be -communicated both to the circulating and to the respiratory apparatus. -Neither the contractile power of the vessels by which in some of -the simpler animals the nutritive fluid is put in motion, nor the -contraction of the rudimentary heart by which in creatures somewhat -higher in the scale a more decided impulse is given to the blood, are -sufficient. A muscular heart, capable of acting with great power, is -now constructed, which is placed in such a position as to enable it to -propel with velocity the whole blood of the body through the myriads -of capillary vessels that crowd every point of the surface of the -branchial leaflets. To bring the water with the requisite degree of -force into contact with this flowing stream, the apparatus of cilia -is wholly inadequate. The water entering by the mouth, is driven with -force, by the powerful muscles of the thorax, through apertures that -lead to the branchial cavities. At the instant that the branchial -leaves receive the currents of water through the appropriate apertures, -the cartilaginous or bony arches which sustain the leaves, separate to -some distance from each other, and to that extent expand the leaves and -proportionally increase the surface exposed to the water: at the same -time, the rush of water through the leaves unfolds and separates each -of the thousand minute filaments of which they are composed, so that -they all receive the full action of the fluid as it flows over them. - -347. After the venous blood of the system has been thus exposed to the -action of the respiratory medium, it is taken up by the vessels called -the branchial veins (fig. CXXIX. 6), which for the reason assigned -(372) are functionally arteries, as the branchial artery (fig. CXXIX. -4) is functionally a vein. The branchial veins uniting together form -the great arterial trunk of the system, (fig. CXXIX. 7) by which the -aërated blood is carried out to every part of the body. - -348. But as if even this extent of apparatus were insufficient to -afford the amount of respiration required by the system of the fish, -the entire surface of its body, which in general is naked and highly -vascular, respires like the branchiæ. Moreover, many fishes swallow -large draughts of air, by which they aërate the mucous surface of -their alimentary canal, which also is highly vascular; and still -further, numerous tribes of these animals are provided with a distinct -additional organ, a bag placed along the middle of the back filled -with air. Commonly this air bag communicates with some part of the -alimentary canal near the stomach, by means of a short wide canal -termed the ductus pneumaticus, but sometimes it forms a simple shut -sac without any manifest opening; at other times it is divided and -subdivided in a perfectly regular manner, forming extended ramified -tubes; while at other times its ramifications present the appearance of -so many pulmonary cells. It is the rudiment of the complex lung of the -higher vertebrata, and it assists respiration; although since in some -tribes it contains not atmospheric air but azote, it is without doubt -subservient to other uses in the economy of the animal. - -349. In water-breathing animals, from the lowest to the highest, it -is then manifest that a special apparatus is provided for, constantly -renewing the streams of water that are brought into contact with their -respiratory surface. - -[Illustration: Fig. CXXX.—_Tracheæ._ - - 1. Integument or skin of the body. 2. Spiracula opening on the - external surface of the skin. 3. Tracheæ, or air tubes, proceeding in - form of radii from the spiracles to 4. the alimentary canal.] - -350. It is the same in aërial respiration. In the simplest form of -aërial respiration the apparatus consists of minute bags or sacs, -placed commonly in pairs along the back, which open for the admission -of the air on the external surface, by small orifices called spiracula -or spiracles (fig. CXXX. 2), at the sides of the body. In the common -earth-worm there are no less than one hundred and twenty of these -minute air vesicles, each of which is provided with an external opening -placed between the segments of the body. In the leech, the number is -reduced to sixteen on each side, which open externally by the same -number of minute orifices. Over the internal surface of these air -vesicles the blood of the system is distributed in minute and delicate -capillaries; and is capable of being aërated by whichever medium may -pass through the external orifices, whether water or air. - -351. In this simple apparatus is apparent the rudiment of the more -perfect aërial respiration by the organs termed tracheæ, minute air -tubes which ramify like blood-vessels through the body (fig. CXXX. 3). -These air tubes open on the external surface by distinct apertures -termed _spiracula_ or _spiracles_ (fig. CXXX. 2), which are commonly -placed in rows on each side of the body (fig. CXXX. 2), with distinct -prominent edges (fig. CXXX. 2), often surrounded with hairs; sometimes -guarded by valves to prevent the entrance of extraneous bodies, and -capable of being opened and closed by muscles specially provided for -that purpose. These tubes, as they proceed from the spiracles to -be distributed to the different organs of the body, often present -the appearance of radii (fig. CXXX. 3), and when traced to their -terminations are found to end in vesicles of various sizes and -figures, but commonly of an elongated and oblong form. These minute -vesicles, when examined by the microscope, are seen to afford still -minuter ramifications, which are ultimately lost in the tissues of the -body. - -352. The tracheæ are composed of three tunics, the external dense, -white and shining; the internal soft and mucous, between which is -placed a middle tunic, dense, firm, elastic, and coiled into a -spiral. By this arrangement the tube is constantly kept in a state of -expansion, and is therefore always open to the access of air. A great -part of the blood of the body, in the extensive class of creatures -provided with this form of respiratory apparatus, including the almost -countless tribes of insects, is not contained in distinct vessels, but -is diffused by transudation through the several organs and tissues of -the body. All the creatures of this class live in air, and possess -great activity; they therefore require a high degree of respiration; -yet they are commonly small in size, and often some portions of -their body consist of exceedingly dense and firm textures; hence to -have localized the function of respiration, by placing the seat of -it in a single organ, would have been impossible, on account of the -disproportionate magnitude which such an organ must have possessed; in -this case it was easier to carry the air to the blood, than the blood -to the air, and accordingly the air is carried to the blood, and, like -the blood in creatures of higher organization, is diffused through -every part of the system. - -[Illustration: Fig. CXXXI.—_Respiratory Organs of the Scorpion._ - - 1. Spiracles. 2. Integument of one half of the body turned back. - 3. Branchial organs. 4. Cells or pouches in which they are lodged. - _a._ One of the respiratory organs removed and magnified, showing - its resemblance to the branchial leaflets, and presenting the - pectinated appearance described in the text.] - -[Illustration: Fig. CXXXII.—_Apparatus of Respiration in the Frog._ - - 1. Trachea. 2. Vesicular lungs. 3. Stomach.] - -353. The next advancement in the ascending scale is, by a step which -obviously connects this higher class with the classes below and above -it. It consists of distinct cells, termed pulmonic cavities (fig. -CXXXI. 4), which communicate externally by spiracula (fig. CXXXI. -1), like tracheæ (351), but which are lined internally by a soft and -delicate membrane plaited into folds, disposed like the teeth of a -comb (pectinated) (fig. CXXXI. _a_), presenting a striking analogy -to the structure of gills (345), and therefore called by the French -writers pneumo-branchiæ. These cavities have the internal form of an -aquatic organ, but they perform the function of air-breathing sacs. In -scorpions (fig. CXXXI. 1) and spiders, this form of the apparatus is -seen in its simplest condition; in the slug and snail it is more highly -developed: for in these latter animals a rounded aperture, placed -near the head, and guarded by a sphincter muscle, that alternately -dilates and contracts, leads to a single cavity, which is lined with a -membrane delicately folded, and overspread with a beautiful net-work of -pulmonary blood-vessels. - -354. Passing from this to the lowest order of the air-breathing -vertebrata (fig. CXXXII.), the apparatus is perfectly analogous, -but more developed. In the reptile, this air-breathing sac, which -now constitutes a true and proper lung, instead of being simple -and undivided, is formed by numerous septa, which traverse each -other in all directions, into vesicles or cells (fig. CXXXII. 2), -which proportionally enlarge the surface for the distribution of -blood-vessels. In the Batrachian reptile, as the frog, salamander, -newt, &c. (fig. CXXXII.), the vesicles, comparatively few in number, -are of large size, and as thin and delicate as soap-bubbles. In the -ophidian reptile, as the serpent, the sac is large and elongated, but -divided only in the upper and back part into vesicles; while in the -Saurian reptiles, as the crocodile, lizard, chamelion, &c., the sac is -comparatively small, but subdivided into very minute vesicles, bearing -a close analogy to the more perfectly organized lung of the higher -animals. - -[Illustration: Fig. CXXXIII.—_Respiratory Apparatus of the Bird, as -seen in the Swan._ - 1. The Trachea. 2. The lungs. 3. Apertures through which air passes - into, 4. Air cells of the body. 5. A bristle passed from one of the - air cells of the body, to the cavity containing the lungs. 6. A - bristle passed from the cavity of the thigh-bone into another air cell - of the body.] - -355. In birds, the next order of vertebrata (fig. CXXXIII.), as in -insects, the class of invertebrated animals which are formed for flight -(352), the respiratory organs extend through the greater part of -the body (fig. CXXXIII. 4). The lungs (fig. CXXXIII. 2), which still -consist of a single pulmonic sac on each side (fig. CXXXIII. 2), are -divided into cells, minute compared with those of the reptile, yet -large compared with those of the quadruped; at the same time numerous -air sacs, similar in structure to those of the lungs, but of larger -size, are distributed over different parts of the body (fig. CXXXIII. -4), which communicate with the air cells of the lungs (fig. CXXXIII. -3); while of these larger sacs, several communicate also with the bones -(fig. CXXXIII. 6), so as to fill with air those cavities which in other -animals are occupied with marrow. - -356. In the mammalia, the highest order of the vertebrata, respiration -is less extended through the system, and is concentrated in a single -organ, the lung, which, though comparatively smaller in bulk than in -some of the lower classes, is far more developed in structure. The lung -in this class consists of a membranous bag, divided into an immense -number of distinct vesicles or cells, in the closest possible proximity -with each other, yet not communicating, and presenting, from their -minuteness, a vast extent of internal surface. This bag is confined to -a distinct cavity of the trunk, the thorax (fig. CXXXIV.), completely -separated from the abdomen by the muscular partition, the diaphragm -(fig. CXXXIV. 10). This organ no longer sends down cells into the -abdomen, nor membranous tubes into the bones; but is concentrated -within the thorax along with the heart (fig. CXXXIV. 2, 3, 8). In -all the orders of this class, the development and concentration of -the organ are in strict proportion to the perfection of the general -organization. - -[Illustration: Fig. CXXXIV.—_View of the Respiratory Apparatus in Man._ - - 1. The Trachea. 2. The right lung. 3. The left lung. 4. Fissures, - dividing each lung into, 5. Large portions termed lobes. 6. Smaller - divisions termed lobules. 7. Pericardium. 8. Heart. 9. Aorta. 10. - Diaphragm separating the cavity of the thorax from that of the - abdomen.] - -357. In man there are two pulmonary bags (fig. CXXXIV. 2, 3), of nearly -equal size, which, together with the heart, completely fill the large -cavity of the thorax (fig. CXXXIV.), their external surface being -everywhere in immediate contact with the thoracic walls. One of these -bags is placed on the right side of the body, constituting the right -lung (fig. CXXXIV. 2), and the other on the left, constituting the left -lung (fig. CXXXIV. 3). Each lung is divided by deep fissures, into -large portions called lobes (figs. CXXXIV. 4, and CXXXV. 6), of which -there are three belonging to the right, and two to the left lung. Each -lobe is subdivided into innumerable smaller parts termed lobules (figs. -CXXXIV. 6, and CXXXV. 6), while the lobules successively diminish in -size until they terminate in minute vesicles that constitute the great -bulk of the organ (fig. CXXXV. 8). - -358. The complete centralization of the respiratory function which thus -takes place in man, renders the apparatus exceedingly complex both on -account of the expedients which are necessary to obtain the requisite -extent of surface, in the small allotted space, and to bring into -contact within that space the fluids that are to act on each other. - -[Illustration: Fig. CXXXV.—_View of the Air Tubes and Lung._ - - 1. The larynx. 2. Trachea. 3. Right bronchus. 4. Left bronchus. 5. - Left lung; the fissures denoted by the two lines which meet at 6, - dividing it into three lobes, and the smaller lines on its surface - marking the division of the lobes into lobules. 7. Large bronchial - tubes. 8. Minute bronchial tubes terminating in the air cells or - vesicles.] - -359. The apparatus consists of a vessel to carry the air to the blood; -a vessel to carry the blood to the air; an organ in which the air and -the blood meet; and an organization by which both fluids are put in -motion. The vessel that carries the air to the blood is the windpipe -(fig. CXXXV. 1, 2); the vessel that carries the blood to the air is -the pulmonary artery (fig. CXL. 7); the organ in which the blood and -the air meet is the lung (fig. CXXXV. 5); the organization which puts -the air in motion, is the structure of bones, cartilage and muscles, -called the thorax (figs. CXLI. and CXLVI.), and the engine that -communicates motion to the blood is the right ventricle of the heart -(fig. CXL. 5). - -360. The windpipe is a tube which extends from the mouth and nostrils -to the lung (figs. CLIII. 1, 9, and CXXXV. 2, 5). It is attached to -the back part of the tongue (fig. CLII. 2, 9), and passes down the -neck immediately before the esophagus, or the tube which leads to the -stomach (fig. CLIII. 9, 12). - -361. In the different parts of its course the windpipe is differently -constructed, performs different offices, and receives different names -according to the diversity of its structure and function. The first -division of it is called the larynx (fig. CXXXV. 1.), the second the -trachea (fig. CXXXV. 2), the third the bronchi (figs. CXXXV. 3, 4, 7, -and CXXXVII.), and the fourth the air vesicles or cells (figs. CXXXV. -8, and CXXXVIII. 2). - -[Illustration: Fig. CXXXVI.—_Posterior View of the Larynx and Trachea._ - - 1. The os hyoides. 2. Thyroid cartilage. 3. Cricoid cartilage. 4. - Arytenoid cartilages, separated from each other. 5. Epiglottis. 6. - Opening of the glottis. 7. Termination of the cartilaginous rings of - the trachea. 8. The ligamentous portion of the trachea. 9. Trachea - laid open, showing its internal mucous surface and follicles, with the - anterior portion of the cartilaginous rings appearing through it.] - -362. The first portion of the windpipe called the larynx (figs. CXXXV. -and CXXXVI), constitutes the organ of the voice. It is situated at -the upper and fore part of the neck (fig. CLIII. 7, 9), immediately -under the bone to which the root of the tongue, called the os hyoides -(figs. CLIII. 6, and CXXXVI. 1), is attached. The larynx forms a -very complex structure, and is composed of a variety of cartilages, -muscles, ligaments, membranes, and mucous glands (fig. CXXXVI. 2, 3, -4, 5). At its upper part is a narrow opening of a triangular figure -called the glottis (fig. CXXXVI. 6), by which air is admitted to and -from the lung. Immediately above this opening is placed the cartilage, -which obtains its name from its situation, _epiglottis_ (fig. CXXXVI. -5), which is attached to the root of the tongue (fig. CLIII. 6, 7), and -which may be distinctly seen in the living body by pressing down the -tongue. - -363. The Epiglottis is highly elastic, and is an agent of no -inconsiderable importance in respiration, deglutition, and speaking. -In respiration it breaks the current of air which rushes to the lungs -through the mouth and nostrils, and prevents it from flowing to the -delicate air cells with too great a degree of force. During the -action of deglutition the epiglottis is carried completely over the -glottis (fig. CLIII. 6, 7, 8), partly because it is necessarily forced -backwards, when the tongue passes backwards in delivering the food to -the pharynx (fig. CLIII. 6, 7, 8, 10), partly because it is carried -backwards by certain minute muscles which act directly upon it, and -perhaps also partly in consequence of its own peculiar irritability. -The moment the action of deglutition has been performed the epiglottis -springs from the aperture of the glottis, partly by its own elasticity, -and partly by the return of the tongue to its former position. During -the act of speaking the column of air which is expelled from the lung, -which rushes through the glottis, and which thus forms the voice, -strikes against the epiglottis, and the voice becomes thereby in some -degree modified. - -[Illustration: Fig. CXXXVII. - - View of the trachea, showing, first, the division of the tube into - the right and left bronchus, and the subdivision of the bronchi into - the bronchial tubes; and secondly, the membranous and cartilaginous - tissues of which the organ is composed.] - -364. The second portion of the windpipe termed the trachea (fig. CXXXV. -2), commences at the under part of the larynx (fig. CXXXV. 1), and -extends as far as the third dorsal vertebra, opposite to which it -divides into two branches which are termed the bronchi (fig. CXXXV. 3, -4, and CXXXVII.). One of these branches, called the right bronchus, -goes to the right lung; the other branch, called the left bronchus, -goes to the left lung (fig. CXXXV. 3, 4). - -365. The trachea of man, like the tracheæ of the air-breathing insect -(351), is composed of three tissues. These tissues differ essentially -from each other in nature, and are widely different in form and -arrangement. They consist of membrane, muscle, and cartilage. - -366. The membranous portion of the human trachea consists of -three coats, the cellular (fig. CXXXVII.), the ligamentous (fig. -CXXXVI. 8), and the mucous (fig. CXXXVI. 9). From the cellular and -ligamentous coats the tube receives its strength, and in some degree -its elasticity; and the mucous coat constitutes the chief seat of -the respiratory function. Between the ligamentous and mucous coats -are placed two sets of muscular fibres; the first, the external set, -passes in a circular direction around the tube; the second set, -placed immediately beneath the circular, is disposed longitudinally, -and collected into bundles. The office of the circular fibres is to -diminish the calibre of the tube, and that of the longitudinal is to -diminish its length. - -367. As the tracheæ of the insect are kept constantly open for the -free admission of air by their middle membranous tunic, dense, firm, -elastic, and coiled into a spiral (351), so, for the accomplishment -of the same purpose, there are placed between the membranous coats -of the human trachea delicate rings of the more highly organized -substance, cartilage (35). These cartilaginous rings amount in the -entire course of the tube to sixteen or eighteen in number (fig. CXXXV. -2); each cartilage being about a line in breadth, and the fourth of a -line in thickness. They never form complete circles, but only a large -segment of a circle (fig. CXXXVI. 7); the circle is incomplete behind -(fig. CXXXVI. 7, 9), because there the esophagus is in direct contact -with the trachea (fig. CLIII. 9, 12), and instead of dense and firm -cartilage, a soft and yielding substance is placed in this situation, -in order that there may be no impediment to the free dilatation of the -esophagus during the passage of the food. - -368. The point at which the bronchi enter the substance of the lung is -called the root of the lung (fig. CXXXV. 3, 4). As soon as the bronchi -begin to divide and ramify within the lung each cartilage, instead of -preserving its crescent shape, is divided into two or three separate -pieces, which nevertheless are still so disposed as to keep the tube -open. With the progressive diminution in the size of the bronchial -branches, their cartilages become less numerous, and are placed at -greater distances from each other, until at length as the bronchi -terminate in the vesicles, the cartilages wholly disappear; and with -the decreasing number and size of the cartilages, the thickness of the -cellular, ligamentous, and muscular coats of the bronchi also lessens, -until at the points where the cartilages disappear, the muscular and -mucous tunics, now reduced to a state of extreme tenuity, alone remain. -The essential constituent of the air vesicles, then, is the mucous -membrane; but there is reason to suppose that the muscular tunic is -likewise continued over these vesicles. - -369. It has been stated that the tracheæ of the insect terminate in the -different tissues of its body by minute vesicles of an oblong form. -The termination of the bronchi in the human lung presents a strikingly -analogous appearance. Malpighi, who with extraordinary talent and -success devoted his life to the investigation of the minute structures -of the various organs of the human body, represents the mucous membrane -of the bronchial tubes as terminating in minute vesicles of unequal -size: and Reisseissen, who has more recently resumed the inquiry and -examined this structure with extreme care, agrees with Malpighi in -stating that the bronchial tubes at their terminal points expand into -minute, delicate, membranous vesicles of a cylindrical and somewhat -rounded figure (fig. CXXXVIII. 2). The bronchial tubes do not divide -to any great degree of minuteness (fig. CXXXVIII. 1), but terminate -somewhat abruptly in the vesicles (fig. CXXXVIII. 2), which though -minute are large enough to be visible to the naked eye (fig. CXXXVIII. -2). Viewed in connexion with the bronchial tubes at their terminal -points, the vesicles present a clustered appearance, not unlike -clusters of currants attached to their stem (fig. CXXXVIII. 2). - -[Illustration: Fig. CXXXVIII.—_View of the Bronchial Tubes terminating -in Air vesicles._ - Fig. 138. - Fig. 139. - External view.—1. Bronchial tube. 2. Air vesicles. Fig. 139. The same - laid open.] - -370. In the insect, for the reason assigned (351), these vesicles are -diffused over the system, aërating every point of the body; in man -they are concentrated in the lung; yet by their minuteness, and by -the mode in which they are arranged, they present in the small space -occupied by this organ, so extended a surface that Hales, representing -the size of each vesicle at the 100dth part of an inch in diameter, -estimates the amount of surface furnished by them collectively at -20,000 square inches. Keil estimating the number of the vesicles at -174,000,000, calculates the surface they present, at 21,906 square -inches. Leiberkuhn at 150 cubic feet; and, according to Monro, it is -thirty times the surface of the human body. - -[Illustration: Fig. CXL. - - 1. The trachea. 2. The right and left bronchus; the left bronchus - showing its division into smaller and smaller branches in the lung, - and the ultimate termination of the branches in the air vesicles. 3. - Right auricle of the heart. 4. Left auricle. 5. Right ventricle. 6. - The aorta arising from the left ventricle, the left ventricle being in - this diagram concealed by the right. 7. Pulmonary artery arising from - the right ventricle and dividing into, 8. The right, and 9. The left - branch. The latter is seen dividing into smaller and smaller branches, - and ultimately terminating on the air vesicles. 10. Branches of one of - the pulmonary veins proceeding from the terminations of the pulmonary - artery on the air vesicles, where together they form the net-work of - vessels termed the Rete Mirabile. 11. Trunk of the vein on its way to - the left auricle of the heart. 12. Superior vena cava. 13. Inferior - vena cava. 14. Air vesicles magnified. 15. Blood-vessels distributed - upon them.] - -371. Such is the structure of the vessel that carries the air to the -blood, and such is the mode of its distribution. - -The vessel that conveys the blood to the air is the pulmonary artery, -the great vessel which springs from the right ventricle of the heart -(fig. CXL. 5). - -The pulmonary artery soon after it issues from the right ventricle of -the heart divides into two branches (fig. CXL. 7, 8, 9), one for each -lung (fig. CXL. 8, 9). Each branch of the pulmonary artery as soon as -it enters its corresponding lung (fig. CXL. 9) divides and ramifies -through the organ in a manner precisely similar to the bronchial -tubes. Every branch of the artery is in contact with a corresponding -branch of the bronchus (fig. CXL. 2), divides as it divides, and -accurately tracks its course throughout (fig. CXL. 2), until the -ultimate divisions of the artery at length reach the ultimate vesicles -of the bronchus (fig. CXL. 2, 10), upon the delicate walls of which -the capillary arteries rest, expand, and ramify, forming a net-work of -vessels, so complex that the anatomist who first observed it, named it -the _Rete Mirabile_, the wonderful net-work, and it is still called -the _Rete Mirabile Malpighi_, or the _Rete Vasculosum Malpighi_ (fig. -CXL. 2, 9, 10). - -372. The blood which has finished its circulation through the system, -returned by the great systemic veins (fig. CXL. 12, 13), to the right -side of the heart (fig. CXL. 3), is driven by the right ventricle (fig. -CXL. 5), into the pulmonary artery (fig. CXL. 7); by the branches of -which (fig. CXL. 8, 9) it is distributed to the air vesicles of the -lungs: consequently the right heart of man bears precisely the same -relation to the lungs, that the single heart of the fish bears to the -branchiæ; the former is a pulmonic, as the latter is a branchial heart; -one half of the double heart of the more highly organized creature is -employed to circulate the venous blood of the system through the lungs, -as the whole of the single heart of the less highly organized animal, -is employed to propel the blood through the branchiæ (368). From the -capillary branches of the pulmonary artery in the Rete Mirabile (fig. -CXL. 9), arises another set of vessels termed the pulmonary veins -(fig. CXL. 10), which receive the blood from the venous vessels spread -out on the air vesicles: for the pulmonary artery is functionally a -vein, since it contains venous blood, though it is nominally an artery -because it carries blood from the heart (269); and in like manner the -pulmonary veins are functionally arteries since they contain arterial -blood, though they are nominally veins because they carry blood to the -heart (272). The branches of the pulmonary arteries are larger in size -and greater in number than those of the pulmonary veins, the reverse of -what is observed in any other part of the body; because the pulmonary -artery contains the blood which is to be acted upon by the air, while -the pulmonary veins merely receive the blood which has been acted upon -by the air, and the former ramifies more minutely than the latter, in -order that the air may act on a larger surface of blood. - -373. In the Rete Mirabile the junction of the air-vessel with the -blood-vessel is accomplished. The combination of these two sets of -vessels constitutes the lung; for the lung is composed of air-vessels -and blood-vessels united, and sustained by cellular tissue, and -inclosed in the thin but firm membrane called the pleura (104 and 105). - -374. Such is the arrangement of that part of the respiratory apparatus -which contains the fluids that are to act on each other. The object -of the remaining portion of it is to produce the movements which are -necessary to bring the fluids into contact. This is accomplished by -the mechanism and action of the thorax and diaphragm (figs. CXLI. and -CXXXIV. 10). - -375. These organs, which invariably act in concert, are so constructed -and disposed, that when in action they give to the chest two alternate -motions, one that by which its capacity is enlarged; and the other that -by which it is diminished. These alternate movements are called the -motions of respiration. The motion by which the capacity of the chest -is enlarged is termed the action of inspiration, and that by which it -is diminished the action of expiration. - -376. The action of inspiration, or that by which the capacity of the -chest is enlarged, is effected by the combined movements of the thorax -and diaphragm; by the ascent of the thorax and by the descent of the -diaphragm. - -377. The osseous portion of the thorax, which has been fully described -(69 _et seq._), consists of the spinal column (fig. CXLI. 1), the -ribs with their cartilages (fig. CXLI. 2, 3), and the sternum (fig. -CXLI. 4). The soft portion of the thorax consists of muscles and -membrane (figs. CXLII., CXLVI., and CXLVII.), together with the common -integuments of the body. The chief boundaries of the cavity of the -thorax before, behind, and at the sides, are osseous, being formed -before by the sternum and the cartilages of the ribs (fig. CXLI. 4, -3); behind by the spinal column and the necks of the ribs (fig. CXLI. -1,2); and at the sides by the bodies of the ribs. Below the boundary is -muscular, being formed by the diaphragm (fig. CXLIII. 3). - -378. Externally the thorax is convex and enveloped by muscle and skin; -internally it is concave (fig. CXLIII. 1), and lined by a continuation -of the same membrane which envelops the lungs, the pleura (104). But -that portion of the pleura which lines the internal wall of the thorax -is called the costal pleura (pleura costalis), in contradistinction to -that which envelops the lungs, which is termed the pulmonary pleura, -or pleura pulmonalis (104). By the costal pleura, a thin but firm and -strong membrane, smooth, polished, and like all the membranes of its -class (serous membrane 30, _et seq._), kept in a state of perpetual -moisture and suppleness, by a fluid secreted at its surface, the -movements of the thorax are facilitated, at the same time that they are -prevented from injuring the delicate organs contained in it. - -379. The moveable parts of the osseous portion of the thorax are the -ribs and sternum. The ribs, though by one extremity tied with exceeding -firmness to the spinal column by ligaments specially constructed, and -admirably adapted for that purpose (figs. LVI. 1, and LVII. 1), and -though attached at their other extremity by their cartilages to the -sternum (fig. LVIII.), are capable of three motions, an upward, an -outward, and a downward motion. - -[Illustration: Fig. CXLI.—_View of the osseous portion of the Thorax._ - - 1. Spinal column. 2. Ribs. 3. Cartilages of ribs. 4. Sternum.] - -380. The ribs form a series of moveable arches, the convexity of the -arches being outwards, and the whole being disposed in an oblique -direction (fig. CXLI. 2). The first rib springs from the vertebral -column at nearly a right angle (fig. CXLI. 2); the acuteness of this -angle increases in succession as the ribs descend from the first to -the last (fig. CXLI. 2); in this manner each rib is inclined obliquely -outwards and downwards, and the obliquity thus given to the general -direction of the ribs augments progressively from above downwards (fig. -CXLI. 2). - -381. In consequence of this conformation and arrangement of the ribs, -every degree of motion which is communicated to them, necessarily -influences the capacity of the space they enclose. If they are moved -upwards they must enlarge that space at the sides, because the -intervals between each other will be increased (fig. CXLI. 2); and from -behind forwards, because the distance between the spinal column and the -sternum (the sternum being protruded forwards with their cartilaginous -extremities) (fig. CXLI. 3, 4), will be increased. If, on the other -hand, they are moved downwards, the capacity of the thorax will be -proportionally diminished in every direction (fig. CXLI.). - -[Illustration: Fig. CXLII. - - View of the intercostal muscles which fill up the interspaces between - the ribs. These muscles consist of a double layer of fibres, the - external and the internal, which cross or intersect each other.] - -382. One part of the action of inspiration consists, then, of this -ascent of the ribs. The ascent of the ribs is effected by the -contraction of a double layer of muscles called the intercostal (fig. -CXLII.), placed in succession between each rib; and which communicate -this motion in the following mode. The first rib is fixed; the second -rib is moveable, but less moveable than the third, the third than the -fourth, and so on through the series: consequently the contraction of -the intercostal muscles (figs. CXLII. and CXLVI. 2) must elevate the -whole series, because the upper ribs afford fixed points for the action -of the muscles; and so, when all these muscles contract together, they -necessarily pull the more moveable arches upwards towards the more -fixed (figs. CXLI. and CXLVI. 2). - -383. But from the oblique direction of the ribs, they cannot ascend -without at the same time protruding forwards their anterior extremities -(fig. CXLI.). Those extremities being attached to the sternum, which -forms the anterior wall of the thorax, they cannot be protruded -forwards without at the same time carrying the sternum forwards with -them (fig. CXLI.). Thus, by this two-fold motion of the ribs, an upward -and consequently an outward motion, the capacity of the thorax is -increased from behind forwards, that is, in its small diameter. - -384. Such is the part of the action, in inspiration, performed by the -motion of the ribs. The remaining part of that action, by far the most -important, consists of the enlargement of the capacity of the thorax -from above downwards, or in its long diameter. This is effected by the -descent of the diaphragm (fig. CXLIII.). - -385. The diaphragm is a circular muscle, forming a complete but -moveable partition between the thorax and the abdomen (figs. CXXXIV. -10, and CXLIII. 3). When not in action its upper surface forms an -arch (figs. CXLIII. 4, and CXLV. 1), the convexity of which is towards -the thorax (figs. CXLIII. 4, and CXLV. 1), and reaches as high as -the fourth rib (fig. CXLV. 1); its under surface, or that towards -the abdomen, is concave (figs. CXXXIV. 10, and CXLV. 1). Its central -portion is tendinous (fig. CXLIII. 4). This central tendinous portion -of the diaphragm, which is in apposition with the heart (fig. CXXXIV. -8), and firmly attached to the pericardium (fig. CXXXIV. 7), is nearly -if not quite immoveable: it is only the lateral or muscular portions -(fig. CXLIII. 4) that are capable of motion. Its central portion is -constructed of dense and firm tendon, and is immoveable, primarily, in -order to afford one of the two fixed points (the ribs affording the -other fixed point), essential to the action of the muscular fibres that -constitute its lateral or moveable portions; and secondarily, in order -to afford a support to the heart, which rests upon this central tendon. -Thus, in consequence of this tendon being rendered absolutely fixed, -the motions of the diaphragm are completely prevented from incommoding -the motions of the heart; the function of respiration from interfering -with the function of the circulation. - -[Illustration: Fig. CXLIII.—_View of the Diaphragm._ - - 1. Cavities of the thorax. 2. Portion of cavity of the abdomen. 3. - Lateral or muscular and moveable portions of the diaphragm. 4. Central - or tendinous and fixed portion of the diaphragm.] - -386. During the action of inspiration the muscular or lateral portions -of the diaphragm contract (fig. CXLIII. 3); its muscular fibres -shorten themselves, and are approximated towards the central tendon -(fig. CXLIII. 2); the consequence is that the whole muscle descends -(fig. CXLIV. 1); passes from the fourth to below the seventh rib -(fig. CXLIV.), loses its arched form and presents the appearance of -an oblique plane (fig. CXLIV.). At the same time the muscles of the -abdomen are protruded forwards (fig. CXLIV. 2), and the viscera -contained in its cavity are pushed downwards. The result of these -movements is, that the capacity of the thorax is enlarged by all the -space that intervenes between the fourth rib (fig. CXLV. 1), and the -lowest point of the oblique plane formed by the diaphragm (fig. CXLIV. -1), together with all that gained by the protrusion of the walls of the -abdomen and the descent of its viscera (fig. CXLIV. 2). - -[Illustration: _Views of the Diaphragm in the different states of -Respiration._ - -Fig. CXLIV. - -Fig. CXLV. - - Fig. 144.—1. Diaphragm in its state of greatest descent in - inspiration. 2. Muscles of the abdomen, showing the extent of their - protrusion in the action of inspiration. Fig. 145.—1. Diaphragm in the - state of its greatest ascent in expiration. 2. Muscles of the abdomen - in action forcing the viscera and diaphragm upwards.] - -387. By the action of the intercostal muscles, then, the capacity of -the thorax is enlarged at the sides and from behind forward, or in its -short diameter; by the action of the diaphragm, the capacity of the -thorax is enlarged from above downwards, or in its long diameter; by -the combined action of both, the capacity of the thorax is enlarged in -every direction, and thus the motion of inspiration is completed. - -388. Expiration, the respiratory motion which alternates with that of -inspiration, consists of the diminution of the capacity of the thorax, -which is effected by the converse motions of the same organs; that is, -by the descent of the ribs and the ascent of the diaphragm. - -389. By the descent of the ribs, the capacity of the thorax is -diminished in its short diameter, because by this motion, the oblique -arches of the ribs are approximated to each other and to the spinal -column, and the sternum is also approximated to the spinal column. -The descent of the ribs is effected first by the elasticity of their -cartilages (fig. CXLI. 2). When the intercostal muscles relax, the -force which raised the ribs ceases to be applied, and that moment the -elasticity of the cartilages comes into play, and carries the ribs down -wards. Secondly, by the contraction of the abdominal muscles (figs. -CXLV. 2, and CXLVI. 6, 7, 8), the direct effect of which is to pull the -ribs downwards (fig. CXLVI. 6, 7, 8). - -390. By the ascent of the diaphragm the capacity of the thorax is -diminished in its long diameter (fig. CXLV. 1). When the diaphragm -ascends, it changes from the figure of an oblique plane (fig. CXLIV. -1), re-assumes its arched form (fig. CXLV. 1), and reaches as high as -the fourth rib (fig. CXLV. 1). At the same time the abdominal muscles -contract (fig. CXLV. 2), and are carried inwards towards the spinal -column (fig. CXLV. 2). The result of these movements is, that the -capacity of the thorax is diminished by all the space that intervenes -between the lowest point of the oblique plane formed by the diaphragm -and the fourth rib (fig. CXLV. 1), and by all the abdominal space lost -by the contraction of the muscles of the abdomen (fig. CXLV. 2). - -[Illustration: Fig. CXLVI.—_View of the principal external Muscles of -Respiration._ - - 1. The muscle called the Scalenus. 2. The muscles called the - Intercostals. 3. Subclavius. 4. The bone called the Clavicle. 5. The - muscle called the Serratus Magnus Anticus. 6. Obliquius Externus. 7. - Rectus. 8. Obliquius Internus.] - -391. The first step necessary to the ascent of the diaphragm is the -relaxation of its muscular fibres. As soon as these fibres are in a -state of relaxation, that is, when the organ has changed from an active -to a completely passive state, the powerful muscles of the abdomen -(fig. CXLVI. 6, 7, 8) contract, and push the abdominal viscera and -the diaphragm with them upwards towards the cavity of the chest (fig. -CXLV. 2); and thus, by the descent of the ribs and the ascent of the -diaphragm, the capacity of the thorax is diminished in every direction, -and the motion of expiration is completed. - -392. Such is the mechanism by which the capacity of the thorax is -alternately enlarged and diminished in the two alternate states of -inspiration and expiration, and the mechanism thus adjusted works in -the following mode. - -393. Expiration succeeding to the state of inspiration, the ribs -descend, the diaphragm ascends, the capacity of the thorax lessens, -and the compressed lungs are forced within the smallest possible -space. Then, inspiration, succeeding to the state of expiration, the -ribs ascend and the diaphragm descends; the capacity of the thorax is -enlarged, and the lungs freed from their pressure expand and fill the -greater space obtained. In about a second and a half after the state -of inspiration has been induced, that of expiration recommences; the -motion of inspiration occupying about double the time of the motion -of expiration, and these alternate conditions succeed each other in a -regular and uniform course, day and night, during our sleeping and our -waking hours to the end of life. - -394. As long as the function is performed in a perfectly natural -manner, a given number of these alternate movements takes place -in a certain time, constituting what is termed the rhythm of the -respiratory motions. These motions perfectly regular in number and -time, are likewise, in the natural state of the function, performed -only with a certain degree of energy; but they are variously modified -at the command of the will; in obedience to numerous sensations and -emotions; in the performance of a great variety of complex actions, -and in different states of disease. These modifying circumstances may -cause the action of inspiration to be more full and deep, and that of -expiration to be more forcible and complete than natural; or they may -cause both movements to be shorter and quicker than common: hence the -distinction of respiration into ordinary and extraordinary. - -395. In ordinary respiration, that is, when the respiratory motions -are perfectly calm and easy, the ascent and descent of the ribs are -scarcely perceptible; the action is confined almost exclusively to the -ascent and descent of the diaphragm. In this condition the only action -of the intercostal muscles is to fix the ribs, and thus to afford one -of the two fixed points which have been shown (385) to be essential -to the action of the diaphragm. But in extraordinary respiration, -that is, when circumstances happen in the economy which require that -those motions should be extended, auxiliary sources can be put in -requisition. There are many powerful muscles situated about the breast, -shoulder and back (fig. CXLVI. and CXLVII.); which are capable of -elevating the ribs and protruding the sternum to a very considerable -extent (figs. CXLVI. 1, 2, 3, 5; and CXLVII. 1, 2, 3). Where, for -example, the fullest inspiration which it is possible to take is -required, the bones of the shoulder and shoulder-joint are firmly -fixed by resting the hands upon the knees, and then every muscle which -has the slightest connexion with the thorax, either before or behind, -capable of raising the ribs, is added to the inspiratory apparatus -(figs. CXLIV. and CXLVII.); at the same time that the abdominal muscles -are relaxed to the utmost degree, in order to facilitate the ascent of -the ribs and the descent of the diaphragm (figs. CXLIV. 2, and CXLVI. -6, 7, 8). If, on the contrary, the fullest possible expiration is -required, the abdominal muscles contract most forcibly (fig. CXLV. 2), -and every other muscle which is capable of still farther depressing the -ribs and of elevating the diaphragm (fig. CXLVI. 6, 7, 8) is called -into intense action. By these forcible and extraordinary efforts the -thorax may be enlarged or diminished double its ordinary capacity. - -[Illustration: Fig. CXLVII.—_View of Muscles which are capable of -assisting in elevating the Ribs and protruding the Sternum, in states -of extraordinary respiration._ - - 1. The muscle called the Great Pectoral. 2. The Small Pectoral. 3. The - Serratus Magnus.] - -396. Such are the mechanism and action of the powers which communicate -to the thorax, the motions by which its capacity is alternately -enlarged and diminished, and by which the requisite impulse is -communicated to the fluids which flow to and from the lungs in the -different states of respiration; that is, by which air and blood flow -to the lungs in the action of inspiration, and from the lungs in the -action of expiration. - -397. The mode in which air is transmitted to the lungs by the -dilatation of the thorax, in the action of inspiration, is the -following. The lungs are in direct contact with the inner surface of -the thorax, and follow passively all its movements. When the volume -of the lungs is reduced to its minimum by the diminished capacity of -the thorax, in the state of expiration, they still contain a certain -bulk of air. As their volume increases with the enlarging capacity of -the thorax in the state of inspiration, this bulk of air having to -occupy a greater space expands. By this expansion of the air in the -interior of the lungs, it becomes rarer than the external air. Between -the rarified air within the lungs, and the dense external air, there -is a direct communication by the nostrils, mouth, trachea, larynx, and -bronchi. In consequence of its greater weight, the dense external air -rushes through these openings and tubes to the lungs and fills the -air vesicles, the current continuing to flow until an equilibrium is -established between the density of the air within the lungs and the -density of the external air; and thus there is established the flow of -a current of fresh air to the air vesicles. - -398. The external air which, in obedience to the physical law that -regulates its motion, thus rushes to the lung in order to fill the -partial vacuum created by the dilatation of the thorax in inspiration, -produces, in passing to the air vesicles, a peculiar sound. When the -lungs are perfectly healthy, and the respiration is performed in a -natural manner, if the ear be applied to any part of the chest, a -slight noise can be distinguished both in the action of inspiration -and that of expiration. A soft murmur, somewhat resembling the sound -produced by the deep inspirations occasionally made by a person -profoundly sleeping. This sound, though appreciable even by the naked -ear, and though produced many times every minute, in every healthy -human being from the first moment of the existence of the first man, -had never been heard, or at least never attended to, until about twenty -years ago, when it was observed by accident. A physician, Dr. Laennec, -of Paris, having occasion to examine a young female labouring under, -as he supposed, some disease of the heart, and scrupling to follow -his first impulse to apply his ear to the chest, chanced to recollect -that solid bodies have the power of conducting sounds better than the -air. Thereupon he procured a quire of paper, rolled it up tightly, -tied it, and then applied one extremity to the patient’s chest and the -other to his ear. Profiting by the result, which was, that he could -hear the beating of the heart infinitely more distinctly than he -could possibly feel it by the hand, he substituted for this first rude -instrument a wooden cylinder, which he called a stethescope or chest -inspector. The attentive and practised use of this instrument is found -to be capable of revealing to the ear all that is passing in the chest -almost as clearly and certainly as it would be visible to the eye, -were the walls of the chest and the tissues of its organs transparent. -Besides the entrance of the air into the lung in inspiration, and its -exit in expiration, even the motion of the blood in the heart, and in -the great blood-vessels, are rendered by this instrument distinctly -manifest to sense; and as the ear which has once become familiar with -the natural sounds produced by these operations in the state of health, -can detect the slightest deviation occasioned by disease, the practical -application of this discovery has already effected for the pathology -of the chest, what the discovery of the circulation of the blood has -accomplished for the physiology of the body. - -399. At the instant that the expanding lung admits the current of air, -it receives a stream of blood. The air rushes through the trachea to -the air vesicles impelled by its own weight; the blood flows through -the trunks of the pulmonary artery to its capillary branches, spread -out on the walls of the air vesicles, driven by the contraction of -the right ventricle of the heart. A current of air and a stream of -blood are thus brought into so close an approximation that nothing -intervenes between the two fluids, but the fine membranes of which -the air vesicles and the capillary branches of the pulmonary artery -are composed, and these membranes being pervious to the air, the air -comes into direct contact with the blood; the two fluids re-act on each -other, and in this manner is accomplished the ultimate object of the -action of inspiration. - -400. On the other hand, by the action of expiration, the bulk of the -lung is diminished; the air vesicles are compressed, and a portion of -the air they contained, forced out of them by the collapse of the lung, -is received by the bronchi, transmitted to the trachea, and ultimately -conveyed out of the system by the nostrils and mouth. - -401. At the same instant that a portion of air is thus expelled from -the lung and carried out of the system, a stream of blood, namely, -blood which has been acted upon by the air, arterial blood, is -propelled from the lung and is borne by the pulmonary veins to the -left side of the heart, to be transmitted to the system (fig. CXL. 10, -11, 4). In this manner, by the simultaneous expulsion from the lung of -a current of air and a stream of blood is accomplished the ultimate -object of the action of expiration. - -402. That blood flows to the lung during the action of inspiration, and -is expelled from it during the action of expiration, is established by -direct experiment. - -403. If the great vessel which returns the blood from the head to the -heart, called the jugular vein, be exposed to view in a living animal, -it is seen to be alternately filled and emptied according to the -different states of inspiration and expiration. - -It becomes nearly empty at the moment of inspiration, because at that -moment the venous stream is hurried forward to the right chambers -of the heart, which in consequence of the general dilatation of the -chest are now expanded to receive it. This may be rendered still more -strikingly manifest to the eye. If a glass tube, blown at the middle -into a globular form, be inserted by its extremities into the jugular -vein of a living animal in such a manner that the venous stream must -pass through this globe, it is found that the globe becomes nearly -empty during inspiration, and nearly full during expiration; empty -during inspiration, because, during this action the blood flows -forwards to the right chambers of the heart; full during expiration, -because during this action the venous stream, retarded in its passage -through the lung, its motion becomes so slow in the jugular vein that -there is time for its accumulation in the glass globe. In the artery, -on the contrary, in which the course of the current is the reverse -of that in the vein, the opposite result takes place. In the carotid -artery the stream is seen to be feeble and scanty during inspiration, -but forcible and full during expiration, and if the artery be divided -the jet of blood that issues from it absolutely stops during the -action of inspiration; and the fuller and deeper the inspiration the -longer is the interval between the jets, while it is during the action -of expiration that the jet is full and strong. - -404. In the course of some experiments performed by Dr. Dill and myself -with a view to ascertain with greater precision the relation between -respiration and circulation, we observed a phenomenon which places -these points in a still more clear and striking light. We happened to -divide a jugular vein. We saw that the vessel ceased to bleed during -inspiration, and that it began to bleed copiously the moment expiration -commenced; the reverse of what uniformly happens in the entire state -of the vessel. The reason is, that the division of the vein cuts off -its communication with the lung, removes it from the influence of -respiration, brings it under the influence, the sole influence of the -powers that move the arterial current, and consequently reverses its -natural condition, and so reverses the manner in which its current -flows; affording a beautiful illustration of the influence of the two -actions of respiration on the two sets of blood-vessels concerned in -the function. - -405. It is then the venous system that is immediately related to -inspiration, and the arterial to expiration. Each respiratory action -exerts a specific influence over its own sanguiferous system, and -the influence of the one action is the reverse of that of the -other, as the two currents they work flow in opposite directions. -The lungs, in inspiration, expand and receive the venous stream; in -expiration, collapse and expel the arterial stream. The expansion of -the lungs in inspiration is thus simultaneous with the dilatation of -the heart: during the inspiratory action both organs receive their -blood. The collapse of the lungs in expiration is simultaneous with -the contraction of the heart: during the expiratory action both organs -expel their blood. - -406. We are thus enabled to form a clear and exact conception of the -mechanism and action of both parts of this complicated function. Almost -all the points connected with the systemic circulation were established -upwards of three hundred years ago (279), but many points connected -with the pulmonic circulation have been established only recently. Our -knowledge of the phenomena of both, and of their mutual relation and -dependence, has been slowly increasing, and is at length tolerably -complete; and now that we understand the exact office and working of -each, we see that the action of the one is not only in harmony with -that of the other, but co-operates with it, and renders it perfect. - -407. But although the main points relative to the influence of -inspiration and expiration over the pulmonary circulation may be said -to be universally admitted, still physiologists are not agreed as to -the relative quantities of blood which are transmitted through the -lungs during these different respiratory states. All are agreed that -the state of inspiration is favourable to the passage of the blood -through the lungs: some maintain that this expansion of the lungs in -inspiration is essential to the pulmonary circulation. There is the -like general consent that the state of expiration retards the flow of -blood through the lungs; by many it is conceived that it completely -stops the current. By these physiologists it is supposed that, during -the action of expiration, the lungs are in a state of collapse; that -they contain a comparatively small portion of air; that in this state -the air vesicles are so compressed, and the pulmonary blood-vessels so -coiled up, that the lungs are absolutely impermeable, and consequently, -that when the blood arrives at the right chambers of the heart, it is -incapable of making its way to the left. This, according to a prevalent -theory, is the immediate cause of death in asphyxia, the state of the -system induced by suspended respiration, as in drowning, hanging, and -suffocation. Death takes place in this condition of the system, it is -argued, because the circulation of the blood is arrested at the right -side of the heart, cannot permeate the lungs, and consequently cannot -reach the left ventricle, to be sent out to supply the organs of the -body. - -408. This opinion, which appears at first view to be favoured by -numerous observations and experiments, has been shown to be fallacious -by a series of decisive experiments, performed by Dr. Dill and myself, -undertaken, as has been stated (404), with the object of ascertaining, -in a more exact manner than had hitherto been done, the relation -between the circulation and respiration. The previously ascertained -fact that the heart continues to beat and the blood to flow several -minutes after the complete suspension of the respiration, or after -apparent death, afforded us the means of pursuing our research. The -details of these experiments are given elsewhere: it is sufficient to -state in this place the main results. - -409. As a standard of comparison, the quantity of blood which flows -through the lungs after apparent death, when the lungs remain in a -perfectly natural state, was previously ascertained. It was found, -after death produced in an animal by a blow on the head, that blood -continued to be transmitted through the lungs for the space of -twenty-five minutes after the complete cessation of respiration. There -passed through the lungs in all five ounces and two drachms of blood. - -410. Respiration was now suspended the instant after a perfectly -natural and easy _inspiration_; there flowed through the lungs four -ounces and five drachms of blood. - -411. Respiration was next suspended the instant after a perfectly -natural and easy _expiration_; there flowed through the lungs two -ounces and seven drachms of blood. - -412. When the trachea of an animal is closed by the pressure of a cord -in suspension, or when an animal is immersed under water, it makes a -succession of violent expirations, by which a large quantity of air is -forced out of the lungs. Hence, when the lungs of an animal that has -perished by hanging or drowning, are examined, they are always found -much reduced in bulk; so much reduced in bulk as to have suggested the -theory that the extreme collapse of the lungs and their consequent -impermeability, is the cause of death in this condition of the system. -On bringing this theory to the test of experiment, it was found that -blood continued to flow through the lungs after apparent death from -suspension, for the space of eleven minutes, and that there passed -through in all five ounces of blood. The comparatively larger quantity -transmitted in this case than when the inspiration and expiration were -perfectly natural, was owing to the larger size of the animal. In the -experiments made with a view to ascertain the relative proportions -of blood transmitted through the lungs in the states of natural -inspiration and expiration, the animals were chosen as nearly as -possible of the same size, and were much smaller than the former. - -413. On examining the quantity of blood that passed through the lungs -after death from submersion, it was found to be very nearly the same -as that which was transmitted after death from suspension. - -414. But the lungs may be brought to a much greater degree of collapse -than that to which they are reduced in hanging and drowning. By -introducing an exhausting syringe into the trachea, a much larger -quantity of air may be drawn out of the lungs than they are capable -of expelling by the most violent efforts of expiration. When, in this -mode, the lungs had been reduced to the greatest possible degree of -collapse, and had been exhausted of all the air that could be drawn out -of them, there flowed through them two ounces of blood. - -415. Such are the results when the lungs are reduced successively -from the moderate degree of collapse incident to a perfectly natural -expiration, to the great degree of collapse incident to suspension -and submersion, and the most extreme degree of collapse which it is -possible to induce by exhaustion. - -416. When the phenomena that take place in the opposite condition of -the lungs were investigated, results were obtained which present a -striking contrast to those which have been stated. On forcing into -the lungs the largest quantity of air which they are capable of -containing without the rupture of the air vesicles, and in this manner -communicating to them the greatest degree of dilatation compatible -with their integrity, it was found that in this state there passed -through them _only three drachms of blood_. - -417. But on fully distending the lungs with water instead of air, the -pulmonary circulation was instantaneously and completely arrested; they -were incapable of transmitting a single drop of blood. On cutting the -aorta across, as in all the preceding experiments, not a particle of -blood was obtained, excepting what issued at a single jet, and which -consisted only of the blood contained in the vessel at the moment the -respiration was stopped. - -418. From these experiments it follows— - -1. That the state of inspiration is favorable to the passage of -the blood through the lungs. In the dilatation of inspiration they -transmitted nearly double the quantity that passed in the collapse of -expiration; or, as four ounces and five drachms are to two ounces and -seven drachms (410 and 411). - -2. That no degree of collapse to which the lungs can be reduced is -capable of wholly stopping the flow of the blood through them. In the -collapse of suspension and submersion they transmitted as much blood, -with the exception of two drachms, as when death was produced by a blow -on the head (412 and 409). In the greatest degree of collapse capable -of being produced by an exhausting syringe, they transmitted half as -much as in the collapse of suspension and submersion (414 and 412). - -3. That it is only a moderate degree of dilatation that is favorable -to the transmission of the blood through the lungs. When the lungs -are over-distended with air, they are capable of transmitting only -an exceedingly small quantity of blood (416); when they are fully -distended with water, they are incapable of transmitting a single drop -of blood (417). In fact they can contain only a certain quantity of -air and blood; and when either of these fluids preponderates, it can -only be by the proportionate exclusion of the other. It will appear -hereafter that these results are capable of applications of the highest -interest and importance in the explanation of numerous phenomena of -health and of disease. - -419. Physiologists have laboured with great diligence to determine the -exact quantity of air and blood which enters and which flows from the -lung at each of the actions of respiration, and they have succeeded in -obtaining tolerably precise results. - -420. The quantity of air capable of being received into the lungs of -an adult man, in sound health, at an inspiration, is determined with -correctness by an instrument constructed by Mr. Green, analagous to -one suggested by Mr. Abernethy. It consists of a tin trough, about a -foot square, and six inches deep, three parts of which are filled -with water. Into this trough is placed a three-gallon glass jar, open -at the bottom, and graduated at the side into pints, half-pints, &c. -To the upper end of the jar a flexible tube is affixed, having at its -connexion a stop-cock. The lungs being emptied, as in the ordinary -action of expiration, and the mouth applied to the end of the flexible -tube, the nostrils being closed by the pressure of the fingers, the -air is drawn out of the jar into the lungs by the ordinary action of -inspiration. When as much air is thus drawn into the lungs as the air -vesicles will hold, the stop-cock is closed, and the quantity of air -inspired is ascertained by the rise of the water, the level of the -water corresponding with the indications marked on the side of the jar. - -421. The quantity of air which a person by a voluntary effort can -inspire at one time is found, as might have been anticipated, to be -different in every different individual. These varieties depend, among -other causes, on the greater or less development of the trunk, on the -presence or absence of disease in the chest, on the degree in which the -lung is emptied of air by expiration previously to inspiration, and -on the energy of the inspiratory effort. The greatest volume of air -hitherto found to have been received by the lung, on the most powerful -inspiration, is nine pints and a quarter. The average quantity which -the lungs are capable of receiving in persons in good health, and free -from the accumulation of fat about the chest, appears to be from five -to seven pints. The latter is about the average quantity capable of -being inspired by public singers. - -422. But these measurements relate to the greatest volume of air which -the lungs are capable of receiving, on the most forcible inspiration -which it is possible to make, after they have been emptied by forcible -expiration, and consequently express the quantity received in -extraordinary, not in ordinary inspiration. The quantity received at an -inspiration easy, natural, and free from any great effort, may be two -pints and a half, but the quantity received at an ordinary inspiration, -made without any effort at all, is, according to former observations -which referred to Winchester measure, about one pint. - -423. The quantity of air expelled from the lung by an ordinary -expiration is probably a very little less than that received by an -ordinary inspiration (456). - -424. No one is able by a voluntary effort to expel the whole contents -of the lungs. Observation and experiment lead to the conclusion that -the lungs, when moderately distended, contain at a medium about twelve -pints of air. As one pint is inhaled at an ordinary inspiration, -and somewhat less than the same volume is expelled at an ordinary -expiration (456), there remain present in the lungs, at a minimum, -eleven pints of air. There is one act of respiration to four pulsations -of the heart; and, as in the ordinary state of health there are -seventy-two pulsations, so there are eighteen respirations in a minute, -or 25,920 in the twenty-four hours. - -425. About two ounces of blood are received by the heart at each -dilatation of the auricles; about the same quantity is expelled from -it at each contraction of its ventricles; consequently, as the heart -dilates and contracts seventy-two times in a minute, it sends thus -often to the lungs, there to be acted upon by the air, two ounces of -blood. It is estimated by Haller that 10,527 grains of blood occupy -the same space as 10,000 grains of water, so that if one cubic inch of -water weigh 253 grains, the same bulk of blood will weigh 266⅓ grains. - -426. It is ordinarily estimated that on an average one circuit of the -blood is performed in 150 seconds; but it is shown (451 and 452) that -the quantity of air always present in the lungs contains precisely a -sufficient quantity of oxygen to oxygenate the blood, while flowing -at the ordinary rate of 72 contractions of the heart per minute, for -the exact space of 160 seconds. It is therefore highly probable that -this interval of time, 160 seconds, is the exact period in which the -blood performs one circuit, and not 150 seconds, as former observations -had assigned. If this be so, then 540 circuits are performed in the -twenty-four hours; that is, there are three complete circulations of -the blood through the body in every eight minutes of time. - -427. But it has been shown (425) that the weight of the blood is to -that of water as 1.0527 is to unity, and that consequently 10,527 -grains of blood are in volume the same as 10,000 grains of water. - -428. From this it results that if in the human adult two ounces of -blood are propelled into the lungs at each contraction of the heart, -that is, 72 times in a minute, there are in the whole body precisely -384 ounces, or 24 pounds avoirdupois, which measure 692.0657 cubic -inches, or within one cubic inch of 20 imperial pints, which measure -693.1847 cubic inches. - -429. By an elaborate series of calculations from these data Mr. -Finlaison has deduced the following general results:— - -1. As there are four pulsations to one respiration (424), there are 8 -ounces of blood, measuring 14.418 cubic inches, presented to 10.5843 -grains of air, measuring 34.24105 cubic inches. - -2. The whole contents of the lungs is equal to a volume of very nearly -411 cubic inches full of air, weighing 127 grains, of which 29.18132 -grains are oxygen. - -3. In the space of five-sixth parts of one second of time, two ounces, -or 960 grains weight of blood, measuring 3⅗ or 3.60451 cubic inches, -are presented for aëration. - -4. Therefore the air contained in the lungs is 114 times the bulk of -the blood presented, while the weight of the blood so presented is 7½ -times as great as the weight of the air contained. - -5. In one minute of time the fresh air inspired amounts to 616⅓ cubic -inches, or as nearly as may be 18 pints, weighing 190½ grains. - -6. In one hour the quantity inspired amounts to 1066⅔ pints, or 2 -hogsheads, 20 gallons, and 10⅔ pints, weighing 23¾ ounces and 31 grains. - -7. In one day it amounts to 57 hogsheads, 1 gallon, and 7¼ pints, -weighing 571½ ounces and 25 grains (454). - -8. To this volume of air there are presented for aëration in one minute -of time 144 ounces of blood, in volume 259½ cubic inches, which is -within 18 cubic inches of an imperial gallon. - -9. In one hour 540 pounds avoirdupois, measuring 449¼ pints, or 1 -hogshead and 1¼ pints;—and - -10. In the twenty-four hours, in weight 12,960 pounds; in bulk 10,782½ -pints, that is, 24 hogsheads and 4 gallons. - -11. Thus, in round numbers, there flow to the human lungs every minute -nearly 18 pints of air (besides the 12 pints constantly in the air -vesicles) and nearly 8 pints of blood; but in the space of twenty-four -hours, upwards of 57 hogsheads of air and 24 hogsheads of blood. - -430. Provision cannot have been made for bringing into contact such -immense quantities of air and blood, unless important changes are to be -produced in both fluids; and accordingly it is found that the air is -essentially changed by its contact with the blood, and the blood by its -contact with the air. - -431. Chemistry has demonstrated the changes effected in the air. -Common atmospheric air is a compound body, consisting of pure air and -of certain substances diffused in it. Pure air is composed of two -gases, azote and oxygen, always combined in fixed proportions. The -substances diffused in pure air, and which are in variable quantity, -are aqueous vapour and carbonic acid gas. These latter substances form -no part of the chemical agents essentially concerned in the process of -respiration. The only constituents of the air which are essentially -concerned in the process of respiration are the two gases, azote and -oxygen, the union of which, in definite proportions, constitutes pure -air. But of these two gases each does not perform the same part in the -function of respiration, nor is each equally necessary to the support -of life. - -432. If a living animal be placed in a vessel full of atmospheric -air, and if all communication of the atmosphere with the vessel be -prevented, the animal in a given time perishes. If an animal be placed -in a vessel full of azote, after a given time it equally perishes; -but if an animal be placed in a vessel full of oxygen, not only is -the function of respiration carried on with far greater energy than -in atmospheric air, but the animal lives a much longer time than in -the same bulk of the latter fluid. If twenty cubic inches of pure -oxygen be capable of sustaining the life of an animal for the space of -fourteen minutes, it can support life in the same bulk of atmospheric -air only six minutes; and if its respiration be confined to either of -these gases, after they have been already respired by another animal -of the same species, the former will live only four minutes; that is, -not longer than when entirely deprived of air. It follows that the gas -which gives to atmospheric air its chief power of sustaining life is -oxygen. - -433. Accordingly it is proved that no animal, from the lowest to the -highest, is capable of sustaining life unless a certain proportion of -oxygen be present in the fluid which it respires. Whether it breathe -by the skin, by gills, or by lungs, whether the respiratory medium be -water or air, the presence of oxygen is alike indispensable. Yet the -life of no animal can be sustained by pure oxygen. If azote be not -mixed with oxygen, evils are produced in the economy which sooner or -later prove fatal. On the other hand, if the proportion of oxygen -be diminished beyond a certain point, drowsiness, torpor, and death -result. Not oxygen alone, then, but oxygen combined with azote, in the -proportion in which nature has united these two fluids to form the -atmosphere of the globe, is indispensable to animal existence. - -434. When the same portion of atmospheric air is repeatedly respired -by an animal, the oxygen contained in it gradually disappears, the gas -lessening with every successive respiration, until at last so small a -quantity remains that it is no longer capable of sustaining the life of -an animal of that class. When respiration has deprived the air of its -oxygen to such an extent, that it can no longer support animal life, -the air is said to be consumed; but, correctly speaking, it is merely -changed in composition, in the proportions in which its constituents -are combined; consequently the effect of respiration is to alter the -chemical composition of the air. - -435. The essential change that takes place consists in the diminution -of the oxygen and the increase of the carbonic acid. When inspired, -atmospheric air goes to the lungs loaded with oxygen; when expired, it -returns loaded with carbonic acid. That the air which returns from the -lungs is loaded with carbonic acid, may be rendered manifest even to -the eye. If a person breathe through a tube into water holding lime in -solution, the carbonic acid contained in the expired air will unite -with the lime and form a white powder analogous to chalk (carbonate of -lime), which being insoluble, becomes visible. - -436. On the other hand, the diminution of oxygen is demonstrated by -chemical analysis. If 100 parts of atmospheric air be successively -respired, until it is no longer capable of supporting life, and if -it be then subjected to analysis, it is found that in place of being -composed of 79 parts azote, 21 oxygen, and a variable quantity of -carbonic acid, sometimes amounting to half a grain per cent., it -consists of 77 parts azote, and 23 carbonic acid. The oxygen is gone, -and is replaced by 23 parts of carbonic acid; at least this is the -ordinary estimate; but different experimentalists differ somewhat in -their account of the absolute quantity of oxygen that disappears, and -of carbonic acid that is generated. - -437. Whatever estimates of the oxygen consumed, and of the carbonic -acid generated, be adopted, they can be taken only as medium -quantities. Dr. Edwards has demonstrated that the absolute quantity -of oxygen consumed in a given time is constantly varying, not only -in animals of different species, but even in the same animal under -different circumstances; insomuch, that there are scarcely two hours -in the day in which the same individual expends precisely the same -quantity. The nature and degree of the exercise taken during the -observation, the condition of the mind, the state of the health, -the kind of food, the temperature of the air, and innumerable other -causes materially influence the quantity of oxygen consumed. When, -for example, the hourly consumption of oxygen, at the temperature -of 54° Fahrenheit, amounted to 1345 cubic inches,[1] it fell, at -the temperature of 79°, to 1210 cubic inches. During the process of -digestion more is consumed than when the stomach is empty; more is -required when the diet is animal than when it is vegetable, and more -when the body and mind are active than when at rest. - - [1] The ordinary consumption of oxygen is, for an adult, 1905 cubic - inches per hour (444). - -438. With regard to the carbonic acid, Dr. Prout has recently made the -remarkable discovery, not only that the generation of this gas differs -according to different circumstances, and more especially according -to particular states of the system; but that the quantity of it which -is produced regularly varies at particular periods of the day. The -quantity generated is always more abundant during the day than during -the night. About daybreak it begins to increase; continues to do so -until noon, when it comes to its maximum, and then decreases until -sunset. The maximum quantity generated at noon exceeds the minimum by -about one-fifth of the whole. If from any cause the relative quantity -be either increased or diminished above or below the ordinary maximum -or minimum, it is invariably diminished or increased in an equal -proportion during some subsequent diurnal period. The absolute quantity -generated is materially diminished by the operation of any debilitating -cause, such as low diet, protracted fasting, or long-continued -exercise, depressing passions and the like. Few circumstances of any -kind increase the quantity produced, and those only in a slight degree. - -439. The changes produced by respiration on the other constituent of -the air, azote, appear at first view to be extremely variable. By -numerous and accurate experiments it is established that the quantity -of this gas is at one time increased; at another diminished, and at -another unchanged. It is probable that there is a constant absorption -and exhalation of it; and that the apparent irregularity is the result -of the preponderance of the one process over the other. When absorption -preponderates, a smaller quantity is found in the air expired than -in that inspired: when exhalation preponderates, a larger quantity -is expired than inspired; and when the absorption and exhalation are -equal, just as much is expired as inspired, and consequently there -appears to be no absorption at all. - -440. Such are the phenomena of respiration, as far as the labours of -physiologists has succeeded in ascertaining them, up to the present -time. But as the estimates of the quantity of air and blood contained -in the lungs were rather matters of conjecture than of demonstration, -and as the quantity of oxygen consumed, of carbonic acid generated, and -of azote absorbed, appeared still not to be determined with exactness, -I requested Mr. Finlaison to apply his power of calculation to the -investigation of this subject, taking as the basis of his calculations -the facts positively and precisely ascertained by experiment and -analysis. This he has done with great care, and has obtained the -following results. - -441. It was formerly estimated that the weight of pure atmospheric air -is 305,000 grains troy for one million of cubic inches; but the latest -authorities assign it to be 310,117 grains. Of this weight of one -million of cubic inches of pure air, - - The weight of the oxygen is 71,809.3 - The weight of the azote is 238,307.7 - ————————— - Total 310,117.0 - -442. But common atmospheric air in its ordinary state contains in 1000 -cubic inches, - - Of pure air 989 - Of the vapour of water 10 - Of carbonic acid gas 1 - -Ten inches of pure air are equal in weight to nine of oxygen. - -Eight inches of azote are equal in weight to seven of oxygen. - -The specific gravity of carbonic acid is to pure air at the rate of -15,277 to 10,000. - -The specific gravity of the vapour of water is to pure air as 6,230 -to 10,000. It follows that a million of cubic inches of air in its -ordinary state weigh 309,111½ grains. - -Carbonic acid gas is composed of oxygen and pure carbon in the -proportion of eight grains of oxygen to three of carbon out of every -eleven grains of carbonic acid. - -443. Though during particular portions in the twenty-four hours, under -circumstances which influence variously the actions of life (437 and -438), the quantity of the oxygen consumed, of carbonic acid generated, -and of azote absorbed, vary (436 to 439), yet it is probable that -the daily consumption, reproduction, and absorption of these gases, -is pretty much the same one day with another. The experiments of -Dr. Edwards clearly show that while these quantities vary to such -an extent, when the observation embraces only a short interval, as -to be scarcely ever the same hour by hour, yet that they lessen as -the interval extends, until at length a nearly exact equilibrium is -established. - -444. Experimental philosophers have not obtained precisely the -same results as to the quantities consumed and reproduced of these -respective gases. At present, therefore, we can only approximate to -the exact amount by taking the average of their observations. The -following are the results of the principal experiments which have -been instituted. The quantity of oxygen consumed by an adult man in -twenty-four hours is, according to - - Menzes 51,840 - Lavoisier 46,048 - Davy 45,504 - Allen and Pepys 39,534 - -The mean of all which is, 45,731.5 inches. - -445. In like manner the quantity of carbonic acid generated in the same -time is, according to - - Davy 38,304 cubic inches. - Allen and Pepys 38,232 “ - The mean of which is, 38,268 “ - -The weight of 38,268 inches of carbonic acid gas is 18,130.1474 grains -troy; and the weight of 45,731½ inches of oxygen is 15,757.9131 grains -troy. - -Now this weight of oxygen must have been derived from the decomposition -of 221,882 cubic inches of common atmospheric air. - -446. It has been shown that, in the state of health, one contraction -of the heart propels to the lungs two ounces of blood; that this -action of the heart is repeated 72 times in one minute; that to every -four actions of the heart there is one action of respiration; that -consequently there are 18 respirations in a minute, and 25,920 in the -twenty-four hours. - -447. From these premises it results that at each action of the heart -there is decomposed of the air inspired, 8.5603 cubic inches, that is, -a quarter of a pint within one-tenth of a cubic inch,—the quarter of a -pint imperial measure being 8.6648 cubic inches. - -448. Previous observation had assigned one pint as the volume of -air ordinarily inhaled at a single inspiration. We now see that the -quantity decomposed is a quarter of a pint. It is, then, an absolute -truth, that of the whole volume of air inspired, one-fourth part only -is decomposed, and that three-fourths, after having been diffused -through the air vesicles of the lungs, are expired without change. - -449. Observation had also assigned 12 pints - of air as the volume constantly present in the - lungs,—that is, 415.9108 cubic inches. - The truth seems to be, - that forty-eight times the - quantity decomposed is - constantly present, namely, 410.8926 cubic inches. - The difference is only 4.0182 cubic inches, - which difference weighs less than 1¼ grains troy. - -450. It is then concluded that the real contents of the lungs is a -volume of 410.8926 cubic inches, which is exactly the 540th part of -221,882 cubic inches, being the whole volume decomposed in twenty-four -hours. But 160 seconds is also exactly the 540th part of the number of -seconds in twenty-four hours. - -451. Of the whole weight of oxygen consumed - in twenty-four hours 15,757.9131 grains, - the 540th part, or the proportion - of 160 seconds, is 29.18132 “ - and 410.8926 cubic inches of - atmospheric air, which, as - above, is the contents of the - lungs, contain of oxygen the - same weight 29.18132 “ - -452. Then, if respiration were suddenly stopped, provision is made by -the quantity of air always retained in the lungs for the oxygenation of -the blood while flowing at the ordinary rate of 72 strokes per minute, -for the exact space of 160 seconds, and for not one instant longer. - -453. This interval of time, then, as has been stated (426), is very -probably the time in which the blood performs one circuit, not 150 -seconds. Then 540 circuits are performed in the twenty-four hours, or -3 circuits in every eight minutes. From this estimate has been deduced -the quantity of blood contained in the whole body of the human adult -(428). - -454. The air inspired in twenty-four hours contains as under:— - - Bulk in Weight in Ingredients. - cubic inches. grains troy. - - Undecomposed, and to be - returned unchanged 665,646 205,758.833, Common air, - - To be decomposed, - containing in solution - - { Pure atmospheric air 219,441 { 15,757.913, Oxygen, - { { 52,294.509, Azote, - { Vapour of water 2,219 428.726, Vapour, - { Carbonic acid gas 222 105.130, Carbonic acid, - Total 887,528 274,345.111, Of all kinds. - -This is, in bulk, 25,607¼ imperial pints, or 57 hogsheads, 1 gallon, -and 7¼ pints, and in weight 571½ ounces and 25 grains. - -455. Now, although the air expired, in consequence of its -recomposition, may have undergone changes in bulk, yet it seems -agreeable to all analogy to suppose that its weight will remain the -same as the weight inhaled. This, however, is not asserted as a truth, -but only assumed, in order to show the result of such a theory. - -456. Then the air expired in twenty-four hours will be as follows:— - - Bulk in Weight in - cubic inches. grains troy. - Given out undecomposed - as before 665,646 205,758.833 - Recomposed carbonic - acid gas 38,268 18,130.147 - Azote liberated 165,927 50,027.405 - Vapour of water as before 2,219 428.726 - ——————— ——————————- - Total 872,060 274,345.111 - -weighing as before, but less in bulk by 446¼ pints: so that for every -100,000 inches expired there were inspired 101,774 cubic inches. - - 457. When from the weight of - carbonic acid gas thus expired, viz., 18,130.147 - we deduct the small portion inhaled - - in solution with the air 105.130 - —————————— - The remainder is 18,025.017 - - The constituent parts of which are, - oxygen derived from the air 13,109.104 - —————————— - And pure carbon derived from the - blood being the difference 4,915.913 - -Thus in the compass of twenty-four hours the blood has produced 10 -ounces and 116 grains very nearly of pure carbon. - - 458. Now, from the oxygen consumed Grains. - in twenty-four hours as above 15,757.913 - - Deduct the weight restored in the - form of carbonic acid gas 13,109.104 - —————————— - The remainder must have been absorbed - into the blood 2,648.809 - - But the weight of carbon given out - being as above 4,915.913 - ————————— - There is still an excess given outweighing 2,267.104 - -459. Some azote, however, is absorbed into the blood (439) as well as -the above ascertained quantity of oxygen. - - The weight of azote so absorbed must - be precisely 2,267.104 - - if the theory be true, that equal weights - are expired and inspired. In - which case, as the weight of the - azote of the air inspired was, as - shown above 52,294.509 - - While the azote expired could only - have weighed 50,027.405 - —————————- - The difference would have been absorbed 2,267.104 - -And thus the weight of carbon discharged by the blood is precisely -compensated by the united weight of the oxygen and azote which it has -absorbed. - -460. Since it appears to be a general truth that one quarter of the air -respired is decomposed, and that the volume of air continually present -in the lungs is sufficient for that consumption of oxygen which is -requisite in 160 seconds of time, _if that volume be_, as is apparent, -48 _times the quantity decomposed_ out of a single respiration, no -error in the quantity of oxygen consumed in the twenty-four hours, -which we have assumed, will affect the time of 160 seconds. For there -being 18 × 60 × 24 respirations, and 60 × 60 × 24 seconds of time in -the twenty-four hours, the 48th part of the first, and the 160th part -of the last product is equally the 540th part of the whole, whatever it -may be. - -461. But if the time in which a circuit of the blood is performed -be, as is most evident, identical with the time in which the whole -volume of air in the lungs is decomposed, and if such period of time -were, as the old observers have assigned, 150 seconds, then it would -follow that only 45 times the quantity of air decomposed at a breath -is present in the lungs, amounting to 385¼ cubic inches, and that the -whole blood in the body is 24 ounces less than on the supposition -of 160 seconds, that is to say, only 360 ounces, or 22½ pounds -avoirdupois. Because the 45th part of 18 × 60 × 24 is the same as the -150th part of 60 × 60 × 24; in each it is the 567th part of the whole. - -462. From the whole of these observations and calculations the -following general results are deduced:— - -1. The volume of air ordinarily present in the lungs is very nearly -twelve pints (449). - -2. The volume of air received by the lungs at an ordinary inspiration -is one pint (422). - -3. The volume of air expelled from the lungs at an ordinary expiration -is a very little less than one pint (456). - -4. Of the volume of air received by the lungs at one inspiration, only -one-fourth part is decomposed at one action of the heart (447). - -5. The fourth part of the volume of air received by the lungs at -one inspiration, and decomposed at one action of the heart, is so -decomposed in the five-sixth parts of one second of time (429.3). - -6. The time in which a circuit of blood is performed is identical with -the time in which the whole volume of air in the lungs is decomposed -(461). - -7. The whole volume of air decomposed in twenty-four hours is 221,882 -cubic inches, exactly 540 times the volume of the contents of the -lungs; 160 seconds being also exactly the 540th part of the number of -seconds in twenty-four hours (450). - -8. The quantity of the blood that flows to the lungs to be acted upon -by the air at one action of the heart is two ounces (425). - -9. This quantity of blood is acted upon by the air in the five-sixth -parts of one second of time (429.3). - -10. One circuit of the blood is performed in 160 seconds of time. Three -circuits are performed every eight minutes; 540 circuits are performed -in the twenty-four hours (453). - -11. The quantity of blood in the whole body of the human adult is 24 -pounds avoirdupois, or 20 pints imperial measure (428). - -12. In the space of twenty-four hours, 57 hogsheads of air flow to the -lungs (429.7). - -13. In the same space of time 24 hogsheads of blood are presented in -the lungs to this quantity of air (424.10). - -14. In the mutual action that takes place between these quantities of -air and blood, the air loses 15,757.9131 grains, or 328¼ ounces of -oxygen, and the blood 10 ounces and 116 grains of carbon (445). - -15. The blood, while circulating through the lungs, permanently retains -and carries into the system—of oxygen, 2,648,809 grams; and of azote, -2,267,104 grains (458). - -16. The ultimate results are two:— - -1st. While the chemical composition of the blood is essentially -changed, its weight amidst all these complicated actions is maintained -steadily the same; for the weight of carbon which is discharged by the -blood is precisely compensated by the united weight of the oxygen and -azote which it absorbs (459). - -2ndly. The distribution of quantities is universally by proportions -or multiples. Thus, of the air inspired, one measure is decomposed -and three measures are returned unchanged: of the air decomposed at a -single inspiration, there are always in store in the lungs precisely -forty-eight measures; and so on in many other cases. The proportions -are not arithmetical, but geometrical. When we compare arithmetical -quantities with each other, we say that one quantity is by so much -greater than another; when we compare geometrical quantities, we say -that one quantity is so many times greater than another. From this -adoption in the distribution of quantities of geometrical proportions -it results that whatever be the size of the animal the ratios remain -uniformly the same, and that thus one and the same law is adapted to -the vital agencies of living beings under every possible diversity of -magnitude and circumstance. - -463. Such are the interesting and important properties and relations -deducible from the phenomena of respiration. The disappearance of -oxygen and azote from the air inspired, and the replacement of the -oxygen that disappears by the production of carbonic acid, and of the -azote by the exhalation of azote, in which, as we have seen, the great -changes wrought by respiration on the air consist, are essentially the -same in all animals, whatever the medium breathed, and whatever the -rank of the animal in the scale of organization. In all, the proportion -of the oxygen of the inspired air is diminished;—in all, carbonic acid -gas is produced. Comparing, then, the ultimate result of the function -of respiration in the two great classes of living beings, it follows -that the plant and the animal produce directly opposite changes in the -chemical constitution of the air. The carbonic acid produced by the -animal is decomposed by the plant, which retains the carbon in its own -system and returns the oxygen to the air. On the other hand, the oxygen -evolved by the plant is absorbed by the animal, which in its turn -exhales carbonic acid for the re-absorption of the plant. - -464. Thus the two great classes of organized beings renovate the air -for each other, and maintain it in a state of perpetual purity. The -plant, it is true, absorbs oxygen during the night as well as the -animal; but the quantity which it gives off in the day more than -compensates for that which it abstracts in the absence of light. This -interesting fact has been recently established by an extended series -of experiments instituted by Professor Daubeney[2] for the express -purpose of investigating this point. - - [2] On the Action of Leaves upon Plants, and of Plants upon the - Atmosphere, by Charles Daubeney, M.D. F.R.S., Professor of Chemistry - and Botany in the University of Oxford. Philosophical Transactions of - the Royal Society of London, for the year 1836. Part I. succession: - the amount of oxygen now evolved was increased from twenty-one to - thirty-nine per cent., and probably had not even then attained the - limit to which the increase of this constituent might have been - brought. From the proportions of the constituent elements of carbonic - acid gas (442) it necessarily follows that, by the mere process of - decomposition, out of every eleven grains of carbonic acid gas eight - grains of oxygen must be liberated, three grains of carbon being - retained by the plant, and consequently that eight grains of oxygen - must be restored to the atmosphere, less only by so much as the plant - itself may absorb. How great, then, must be the production of oxygen - by an entire tree under favourable circumstances; that is, when animal - respiration and animal putrefaction present to it an abundant supply - of carbonic acid on which to act! - -465. From the general tenor of these experiments, it appears that, -in fine weather and as long as the plant is healthy, it adds to the -atmosphere an amount of oxygen not only sufficient to compensate for -the quantity it abstracts in the absence of light, but to counterpoise -the effects produced by the respiration of the whole animal kingdom. -The result of one of these experiments will convey some conception -of the amount of oxygen evolved. A quantity of leaves about fifty in -number were enclosed in a jar of air; the surface of all the leaves -taken together was calculated at about three hundred square inches; by -the action of these leaves on the carbonic acid introduced into the -jar, there was added to the air contained in it no less than twenty-six -cubic inches of oxygen. As there was reason to conclude that the -evolution of oxygen, in the circumstances under which this experiment -was performed, was considerably less than it would have been in the -open air, several plants were introduced into the same jar of air in -pretty quick - -466. This influence, says Professor Daubeney, is not exerted -exclusively by plants of any particular kind or description. I have -found it alike in the monocotyledonous and dycotyledonous; in such as -thrive in sunshine and those which prefer the shade; in the aquatic -as well as in those of a more complicated organization. How low in -the scale of vegetable life this power extends is not yet exactly -ascertained; the point at which it stops is probably that at which -there ceases to be leaves. - -467. From the whole, then, it appears that the functions of the plant -have a strict relation to those of the animal; that the plant, created -to afford subsistence to the animal, derives its nutriment from -principles which the animal rejects as excrementitious, and that the -vegetable and animal kingdoms are so beautifully adjusted, that the -very existence of the plant depends upon its perpetual abstraction of -that, without the removal of which the existence of the animal could -not be maintained. - -468. The changes produced upon the blood by the action of respiration -are no less striking and important than those produced upon the air. -The blood contained in the pulmonary artery, venous blood (fig. -140-7.), is of a purple or modena red colour: the moment the air -transmitted to the blood by the bronchial tubes comes into contact with -it, in the rete mirabile (fig. 140-10.), this purple blood is converted -into blood of a bright scarlet colour. Precisely the same change is -produced upon the blood by its contact with the air out of the body. -If a clot of venous blood be introduced into a vessel of air, the clot -speedily passes from a purple to a scarlet colour; and if the air -contained in the vessel be analyzed, it is found that a large portion -of its oxygen has disappeared, and that the oxygen is replaced by a -proportionate quantity of carbonic acid. If the clot be exposed to pure -oxygen, this change takes place more rapidly and to a greater extent; -if to air containing no oxygen, no change of colour takes place. - -469. The elements of the blood upon which a portion of the air exerts -its action are carbon and hydrogen. The oxygen of the air unites with -the carbon of the blood and forms carbonic acid, and this gas is -expelled from the system by the action of expiration. The constituent -of the blood which affords carbon to the air would appear to be chiefly -the red particles. The other portion of the oxygen of the air unites -with the hydrogen which is expelled with the carbonic acid in the form -of aqueous vapour. The direct and immediate effect of the action of -respiration upon the blood is then to free it from a quantity of carbon -and hydrogen. - -470. Physiologists are not agreed whether the union of the oxygen of -the air with the carbon of the blood takes place in the lungs or in the -system. Some experimentalists maintain that the oxygen which disappears -from the air, and that which is contained in the carbonic acid, are -exactly equivalent, so that no oxygen can be absorbed. According to -this view, which has been clearly shown to be incorrect (459), the -effect of respiration is merely to burn the carbon of the blood, just -as the oxygen of the air burns wood in a common fire, the result -of this combustion being the generation of carbonic acid, which is -expelled from the system the moment it is formed. - -471. The theory of Dr. Crawford is essentially the same, which supposes -that venous blood contains a peculiar compound of carbon and hydrogen, -termed _hydro-carbon_, the elements of which unite in the lungs with -the oxygen of the air, forming water with the one and carbonic acid -with the other. Mr. Cooper, for many years past, has taught the same -doctrine in his lectures, without any knowledge of the fact that -Crawford had suggested a similar modification of his theory. - -472. It is now established that more oxygen disappears than is -accounted for by the amount of carbonic acid that is generated. The -experiments of Dr. Edwards had already shown this in so decisive -a manner that physiologists almost universally admitted it as an -ascertained fact. The calculations of Mr. Finlaison, to whom the -opinions of physiologists on this point were unknown, have now -determined the precise amount of oxygen (444 _et seq._), and the -probable amount of azote (459) absorbed. By many physiologists it is -supposed that the oxygen retained by the lungs, as long as it remains -in this organ, enters only into a state of loose combination with the -blood; that in this state of loose combination, it is carried from -the lungs into the general system; and that it is only in the system -that the union becomes intimate and complete. According to this view, -the lungs are merely the portal by which the substances employed in -respiration are received and discharged, the essential changes induced -taking place in the system. That it is through the lungs that the -oxygen required by the system is received, is an opinion founded on -experiments no less exact than decisive; it is in accordance with the -most probable theory of the production and distribution of animal heat -(chap. ix.); and the preponderance of evidence in its favour is so -great that, in the present state of our knowledge, it may be considered -as established; but it will appear hereafter that the lungs are by no -means passive in the process, and that, physiologically considered, -they as truly constitute a gland secreting carbonic acid gas as the -liver is a gland secreting bile. - -473. Such are the main facts which have been ascertained relative to -respiration, as far as this function is performed by the lungs. But -the liver is a respiratory organ as well as the lungs. It decarbonizes -the blood. It carries on this process to such an extent, that some -physiologists are of opinion that the liver is the chief organ by -which the decarbonization of the blood is effected. The following -considerations show that whatever be the relative amount of its action, -the liver powerfully co-operates with the lungs in the performance of a -respiratory function. - -1. The liver, like the lungs, is a receptacle of venous blood; blood -loaded with carbon. The great venous trunk which ramifies through the -lungs is the pulmonary artery, containing all the blood which has -finished its circuit through the system. The great venous trunk which -ramifies through the liver is the vena portæ, containing all the blood -which has finished its circuit through the apparatus of digestion. The -liver is a secreting organ, distinguished from every other secreting -organ by elaborating its peculiar secretion from venous blood. Carbon -is abstracted from the venous blood that flows through the lungs in the -form of carbonic acid; carbon is abstracted from the venous blood that -flows through the liver in the form of bile. - -2. All aliment, but more especially vegetable food, contains a large -portion of carbon, more it would appear than the lungs can evolve. The -excess is secreted from the blood by the liver, in the form of resin, -colouring matter, fatty matter, mucus, and the principal constituents -of the bile. All these substances contain a large proportion of carbon. -After accomplishing certain secondary purposes in the process of -digestion, these biliary matters, loaded with carbon, are carried out -of the system together with the non-nutrient portion of the aliment. -In the decarbonizing process performed by the lungs and the liver, -the chief difference would seem, then, to be in the mode in which the -carbon that is separated is carried out of the system. In the lungs -it is evolved, as has been stated, in union with oxygen in the form -of carbonic acid; in the liver, in union with hydrogen in the form of -resin and fatty matter. - -3. Accordingly, in tracing the organization of the animal body from the -commencement of the scale, it is found that among the distinct and -special organs that are formed, the liver is one of the very first. It -would appear to be constructed as soon as the economy of the animal -requires a higher degree of respiration than can be effected by the -nearly homogeneous substance of which, very low down in the scale, -the body is composed. Invariably through the whole animal series, the -magnitude of the liver is in the inverse ratio to that of the lungs. -The larger, the more perfectly developed the lungs, the smaller the -liver; and conversely, the larger the liver the smaller and the less -perfectly developed the lungs. This is so uniform that it may be -considered as a law of the animal economy. In the highly organized -warm-blooded animal, with its large lungs, divided into numerous lobes, -and each lobe composed of minute vesicles respiring only air, the -magnitude of the liver compared with that of the body is small. In the -less highly organized animal of the same class, with its smaller and -less perfectly developed lung, respiring partly air and partly water, -the liver increases as the lung diminishes in size. In the reptile -with its little vesicular lung, divided into large cells, the liver is -proportionally of greater magnitude. In the fish which has no lung, -but which respires by the less highly organized gill, and only in the -medium of water, the proportionate size of the liver is still greater; -but in the molluscous animal, in which the lung or the gill is still -less perfectly developed, the bulk of the liver is prodigious. - -4. In all animals the quantity of venous blood which is sent to the -liver increases, as that transmitted to the lung diminishes. In the -higher animal the great venous trunk which ramifies through the liver -(the vena portæ) is formed by the veins of the stomach, intestines, -spleen, and pancreas, which are the only organs that transmit their -blood to the liver. In the reptile, besides all these organs, the hind -legs, the pelvis, the tail, the intercostal veins forming the vena -azygos and in some orders of this class, even the kidneys also send -their blood to the liver; but in the fish, in addition to all the -preceding organs, the apparatus of reproduction likewise transmits its -blood to the liver. The very formation of the venous system in the -different classes of animals seems thus to point to the liver as a -compensating and supplementary organ to the lung. - -5. The permanent organs in the lower animal are a type of the -transitory forms through which the organs of the higher animal pass -in the progress of their growth. Thus the liver of the human fœtus is -of such a disproportionate size, as to approximate it closely to that -of the fish or of the reptile. After the birth of the human embryo, -respiration is effected in part by the lung; but before birth the lung -is inactive, no air reaches it; it contributes nothing to respiration; -the decarbonizing action of the blood is accomplished, not by the lung, -but by the liver; hence the prodigious bulk of the fœtal liver and its -activity in the secretion of bile, and especially towards the latter -months of pregnancy, when all the organs are greatly advanced in size -and completeness. - -6. Pathology confirms the evidence derived from comparative anatomy and -physiology. When the function of the lung is interrupted by disease, -the activity of the liver is increased. In inflammation of the lung -(pneumonia); in the deposition of adventitious matter in the lung -(tubercles), by which the air vesicles are compressed and obliterated, -the lung loses the power of decarbonizing the blood in proportion to -the extent and severity of the disease with which it is affected. In -this case the secretion of bile is increased. In diseases of the heart -the liver is enlarged. In the morbus cæruleus (516) the liver retains -through life its fœtal state of disproportion. - -7. In the last place, there is a striking illustration of the -respiratory action of the liver, in the vicarious office which it -performs for the lung, during the heat of summer in cold, and all the -year round in hot climates. In the heat of summer, and more especially -in the intense and constant heat of a warm climate, in consequence of -the rarefaction of the air, respiration by the lung is less active -and efficient than in the winter of the cold climate. During the -exposure of the body to this long-continued heat, there is a tendency -to the accumulation of carbon in the blood. An actual accumulation is -prevented, by an increased activity in the secretion of bile, to which -the liver is stimulated by the heat. In order to obtain the material -for the formation of this unusual quantity of bile, it abstracts -carbon largely from the blood; to this extent it compensates for the -diminished efficiency of the lung, and thus removes through the vena -portæ that superfluous carbon which would otherwise have been excreted -through the pulmonary artery. - -474. Taking life in its most extended sense, as comprehending both the -circles it includes, the organic and the animal (vol. i. chap. 2), it -may be said to have three great centres, of which two relate to the -organic, and the third to the animal life (vol. i. chap. 2). The two -centres which relate to the organic life are the systems of respiration -and circulation; the third, which relates to the animal life, is the -nervous system. Of the organic life, the lungs and the heart are the -primary seats; of the animal, the brain and the spinal cord. Between -each the bond of union is so close, that any lesion of the one -influences the other, and neither can exist without the support of -all. They form a triple chain, the breaking of a single link of which -destroys the whole. - -475. But of these three great centres of life, upon which all the -other vital phenomena depend, the most essential is respiration; hence, -to consider the relation of this function to the others, is to take the -most comprehensive view of the uses which respiration serves in the -economy. - -476. The first and most important use of the function of respiration -is to maintain the action of the organs of the animal life. It has -been shown (vol. i. chap. 2) that the organic is subservient to the -animal life, and that to build up the apparatus of the latter, and to -maintain it in a condition fit for performing its functions, is the -final end of the former. The direct and the immediate effect of the -suspension of respiration is the abolition of both functions of the -animal life—sensation and voluntary motion. If a ligature be placed -around the trachea of a living animal so as completely to exclude all -access of air to the lungs, and if the carotid artery be then opened, -and the blood allowed to flow, the bright scarlet-coloured blood -contained in the artery is observed gradually to change to a purple -hue. The exact point of time at which this change begins may be noted. -It is seen to assume a darker tinge at the end of half a minute; at -the end of one minute its colour is still darker, and at the end of -one minute and a half, or at most two minutes (426), it is no longer -possible to distinguish it from venous blood. As soon as this change of -colour begins to be visible the animal becomes uneasy; his agitation -increases as the colour deepens; and when it becomes completely dark, -that instant the animal falls down insensible. If in this state of -insensibility air be readmitted to the lungs, the dark colour of the -blood rapidly changes to a bright scarlet, and instantly sensation -and consciousness return. But if, on the contrary, the exclusion of -the air be continued for the space of three minutes from the first -closing of the trachea, the animal not only remains to all appearance -dead, but in general no means are capable of recovering him from the -state of insensibility; and if the exclusion of the air be protracted -to four minutes, apparent passes into real death, and recovery is no -longer possible. It follows that one of the conditions essential to the -exercise of the function of the brain is, that this organ receive a due -supply of arterial blood. - -477. The second use of the function of respiration is to afford -blood capable of maintaining the muscles in a condition fit for the -performance of their peculiar office, that of contractility. The -closure of the trachea not only abolishes sensation, but the power -of voluntary motion: sensation and motion are lost at once: on the -re-admission of air to the lungs, both functions are regained at -once: it follows that the process of respiration is as essential -to the action of the muscle as to that of the brain. “By arterial -blood,” says Young, “the muscles are furnished with a store of that -unknown principle by which they are rendered capable of contracting.” -“The oxygen absorbed by the blood,” says Spalanzani, “unites with -the muscular fibres and endows them with their contractility.” It -is more correct to say, respiration takes carbon from the blood and -gives it oxygen, and by this means endows the blood with the power of -maintaining the contractility of the muscular fibre. - -478. But respiration is as essential to the action of the organs of -the organic life as to those of the animal. In a short time after -the respiration ceases, the circulation stops. When the blood is no -longer changed in the lungs, it soon loses all power of motion in the -system; because venous blood paralyses the muscular fibres of the heart -as of the arm. When the left ventricle of the heart sends out venous -blood to the system, it propels it into its own nutrient arteries, -as well as into the other arteries of the body; into the coronary -arteries, as well as into the other branches of the aorta; the heart -loses its contractility, for the same reason as every muscle under -the like privation; because venous instead of arterial blood flows in -its nutrient arteries; and the circulation stops when the heart is no -longer contractile, because the engine is destroyed that works the -current. - -479. Venous blood consists of chyle, the nutritive fluid formed from -the aliment; of lymph, a fluid composed of organic particles, which -having already formed an actual part of the solid structures of the -body, are now returning to the lungs to receive a higher elaboration; -and of blood which, having completed its circuit through the system, -and there given off its nutrient and received excrementitious matter, -is now returning to the lungs for depuration and renovation. These -commingled fluids, on parting in the lungs with carbonic acid and -water, and on receiving in return oxygen and azote, are converted into -arterial blood; that is, blood more coagulable than venous, and richer -in albumen, fibrin, and red particles, the proximate organic principles -of all animal structures. The rich and pure stream thus formed is sent -out to the various tissues and organs, from which, as it flows to -them, they abstract the materials adapted to their own peculiar form, -composition, and vital endowments. By the reception of these materials -the organs are rendered capable of performing the vital actions which -it is their office to accomplish. And thus the processes of digestion, -absorption, secretion, nutrition, formation, reproduction, all the -processes included in the great organic circle, no less than muscular -action and nervous energy, depend on receiving a due supply of arterial -blood. All these actions, like the faculties of the animal life, cease -totally and for ever in a few minutes after the formation of this vital -fluid has been stopped by the suspension of respiration. - -480. In the last place, the depurating process effected by respiration -is necessary to prevent the decomposition of the blood, and eventually -that of the body. The first step in the spontaneous decomposition -of animal matter consists in the loss of a portion of its carbon, -which, uniting with the oxygen of the atmosphere, forms carbonic -acid; precisely the same thing that takes place in the process of -respiration. The bodies of all animals, of worms, insects, fishes, -birds, and mammalia, deoxidate the air and load it with carbonic -acid after death, some of them nearly as much as during life; and -this before any visible marks of decomposition can be traced. It is -probable that the cause which more immediately operates in preventing -the decomposition of the body is the abstraction of a part of the -carbon of the blood; that were these carbonaceous particles allowed -to accumulate, they would produce a tendency to decomposition, which -would terminate in complete disorganization; and consequently, that one -main object of the process of respiration is to afford blood not only -capable of nourishing and sustaining the organs, but of maintaining -their integrity, by removing noxious matter, the presence of which -would subvert their composition and lead to their entire decomposition. - -481. The ultimate object of respiration, then, is to prepare and to -preserve in a state of purity a fluid capable of affording to all the -parts of the body the materials necessary to maintain their vital -endowments. By the exhalation of oxygen and water, and the absorption -of carbon, under the agency of light, the plant elaborates such a fluid -from its nutritive sap, and out of this elaborated sap forms terniary -combinations, the organic elements of all vegetable solids. By the -absorption of oxygen and azote, and the exhalation of carbonic acid -and water, probably under the influence of electricity, conducted and -regulated by the nervous system, the animal elaborates such a fluid -from its aliment, and out of this elaborated fluid forms quaternary -combinations, albumen, and fibrin, the organic elements of all animal -solids. - - - - -CHAPTER IX. - - Of the temperature of living bodies—Temperature of plants—Power - of plants to resist cold and endure heat—Power of generating - heat—Temperature of animals—Warm-blooded and cold-blooded - animals—Temperature of the higher animals—Temperature of the different - parts of the animal body—Temperature of the human body—Power of - maintaining that temperature at a fixed point whether in intense - cold or intense heat—Experiments which prove that this power is a - vital power—Evidence that the power of generating heat is connected - with the function of respiration—Analogy between respiration and - combustion—Phenomena connected with the functions of the animal body, - which prove that its power of generating heat is proportionate to - the extent of its respiration—Theory of the production of animal - heat—Influence of the nervous system in maintaining and regulating the - process—Means by which cold is generated, and the temperature of the - body kept at its own natural standard during exposure to an elevated - temperature. - - -482. Closely connected with the function of respiration, is the power -which all living beings possess of resisting within a certain range -the influence of external temperature. The plant is warmer than the -surrounding air in winter, and colder in summer. A thermometer placed -at the bottom of a hole bored into the centre of a living tree, -precaution being taken to keep off as much as possible all external -influence either of heat or cold, does not rise and fall according to -the changes of external temperature; but rises when the external air -is cold, and falls when it is warm. Thus, in a cold day in spring, the -wind being north, at six o’clock in the evening, the temperature of -the external air being 47°, that of a tree was 55°. On another cold -day in the same month, there being snow and hail, and the wind in the -north-east, at six o’clock in the evening, the external temperature -being 39°, that of the tree was 45°. On the contrary, in one -experiment, when the temperature of the air was 57½°, that of the tree -was only 55°; and when the temperature of the air was 62°, that of the -tree was 56°. - -483. These experiments afford an explanation of circumstances familiar -to common observation. Every one has noticed that the snow which -falls on grass and trees melts rapidly, while that on the adjoining -gravel walks often remains a long time unthawed. Moist dead sticks are -constantly found frozen hard in the same garden with tender growing -twigs, which are not in the least degree affected by the frost. Every -winter in our own climate tender herbaceous plants resist degrees of -cold which freeze large bodies of water. - -484. But the colder, and the warmer the climate, the more strikingly -does the plant exemplify the power with which it is endowed of -resisting external temperature. In the northern parts of America the -temperature is often 50° below zero; yet, though exposed to this -intense degree of cold, the spruce fir, the birch, the juniper, &c. -preserve their vitality uninjured. From numerous experiments which -have been performed expressly with a view to ascertain this point, it -is found that a plant which has been once frozen is invariably dead -when thawed. It is also proved by direct experiment, that if the sap -be removed from its proper vessels, it freezes at 32°, the ordinary -freezing point. In the northern parts of America, then, the plant must -preserve in its living vessels its sap from freezing, when exposed to -a temperature of 50° below zero; which sap out of these vessels would -congeal at the ordinary freezing point; that is, the plant of this -climate is endowed with the power of resisting a degree of cold ranging -from the ordinary freezing point to 50° below zero; a property which -can be referred only to a vital power, by the operation of which the -plant generates within itself a degree of heat sufficient to counteract -the external cold. - -485. The opposite faculty of resisting the influence of external heat -is exemplified by the trees and shrubs of tropical climates, often -surrounded by a temperature of 104°, which they resist just as the -plant of the northern clime resists the intense degrees of cold to -which it is exposed. - -486. That the plant is endowed with the power of generating heat is -demonstrated by the phenomena which attend the performance of some of -its vital processes, such as those of germination and flowering. During -the germination of barley, the thermometer was observed to rise in the -course of one night to 102°. The bulb of a thermometer applied to the -surface of the spadix of an arum maculatum, indicated a temperature -7° higher than that of the external air; but in an arum cordifolium, -at the Isle of France, a thermometer placed in the centre of five -spadixes stood at 111°; and in the centre of twelve at 121°, though the -temperature of the external air was only 66°. - -487. Animals indicate in a still more striking degree the power of -generating heat. The lower the animal in the scale of organization, -indeed, the nearer it approaches to the plant in the comparative -feebleness of this function. The heat of worms, insects, crustacea, -mollusca, fishes, and amphibia, is commonly only two or three degrees -above that of the medium in which they are immersed. Absolutely -colder than the higher animals, they are at the same time incapable -of resisting any considerable changes in the temperature of the -surrounding medium, whether from heat to cold or from cold to heat. -The higher animals, on the contrary, maintain their heat steadily at a -fixed point, or very nearly at a fixed point, however the temperature -of the surrounding medium may change. Hence animals are divided -into two great classes, the cold-blooded and the warm-blooded. The -temperature of the cold-blooded is lower than that of the warm-blooded, -and it varies with the heat of the surrounding medium; the temperature -of the warm-blooded is higher than that of the cold-blooded, and -it remains nearly at the same fixed point, however the heat of the -surrounding medium may change. - -488. The temperature natural to the higher animals differs somewhat -according to their class. The temperature of the bird is the highest, -and is pretty uniformly about 103° or 104°; that of the mammiferous -quadruped is 100 or 101°; that of the human species is 97° or 98°. - -489. The temperature of the animal body is not precisely the same in -every part of it. The ball of the thermometer introduced within the -rectum of the dog stood at 100½; within the substance of the liver at -100¾; within the right ventricle of the heart at 101°, and within the -cavity of the stomach at 101°. In the brain of the lamb it stood at -104°; in the rectum at 105°; in the right ventricle of the heart, and -in the substance of the liver and of the lungs, at 106°; and in the -left ventricle of the heart at 107°. - -490. The temperature natural to the human body is 98°. When the human -body is surrounded by an atmosphere at the temperature of 30°, it -must have its heat rapidly extracted by the cold medium; yet the -temperature of the body, however long it remain exposed to such a -degree of cold, does not sink, but keeps steadily at its own standard. -But animals which inhabit the polar regions are often exposed to a cold -40° below zero. The temperature of Melville Island is so low during -five months of the year that mercury congeals, and the temperature is -sometimes 46° below zero; yet the musk oxen, the rein deer, the white -hares, the polar foxes, and the white bears which abound in it maintain -their temperature steadily at their own natural standard. - -491. The power which the higher animal possesses of resisting heat -is still more remarkable than its power of resisting cold. On taking -rabbits and guinea-pigs from the temperature of 50°, and introducing -them very rapidly to the temperature of 90°; it was found that the -animals acquired only two or three degrees of heat. How different -the result when the cold-blooded animal is subjected to the same -experiment! The temperature of the surrounding air being 45°, a -thermometer introduced into the stomach of a frog rose to 49°. The -frog being then put into an atmosphere made warm by heated water, and -allowed to stay there twenty minutes, the thermometer on being now -introduced into the stomach rose to 64°. - -492. But the human body may be actually placed in a temperature of 60° -above that of boiling water, not only without sustaining the slightest -injury, but without having its own temperature raised excepting by two -or three degrees. The attention of physiologists was first directed -to this curious fact by some remarkable circumstances related by the -servants of a baker at Rochefoucault, who were in the habit of going -into the heated ovens in order to prepare them for the reception of -the loaves. In performing this service, the young women were sometimes -exposed to a temperature as high as 278°. It was stated that they could -endure this intense heat for twelve minutes, without any material -inconvenience, provided they were careful not to touch the surface -of the oven. Subsequently Drs. Fordyce, Blagden, and others, with a -view to ascertain the exact facts, entered a chamber, heated to a -temperature much above that of boiling water, and some of the phenomena -observed during these experiments are highly curious. - -493. In the first room entered by these experimentalists, the highest -thermometer varied from 132° to 130°; the lowest stood at 119°. Dr. -Fordyce having undressed in an adjoining cold chamber, went into the -heat of 119°; in half a minute the water poured down in streams over -his whole body, so as to keep that part of the floor where he stood -constantly wet. Having remained here fifteen minutes, he went into the -heat of 130°; at this time the heat of his body was 100°, and his pulse -beat 126 times in a minute. While Dr. Fordyce stood in this situation a -Florence flask was brought in by his order, filled with water heated -to 100°, and a dry cloth with which he wiped the surface of the flask -quite dry; but it immediately became wet again, and streams of water -poured down its sides, which continued till the heat of the water -within had risen to 122°, when Dr. Fordyce went out of the room, after -having remained fifteen minutes in a heat of 130°: just before he left -the room his pulse made 129 beats in a minute; but the heat under his -tongue and in his hand did not exceed 100°. - -494. In a subsequent experiment the chamber was entered when the -thermometer stood above 211°. The air heated to this degree, says -Dr. Blagden, felt unpleasantly hot; but was very bearable. Our most -uneasy feeling was a sense of scorching in the face and legs; our legs -particularly suffered very much, by being exposed more fully than any -other part to the body of the stove, heated red hot by the fire within. -Our respiration was not at all affected; it became neither quick nor -laborious; the only difference was a want of that refreshing sensation -which accompanies a full inspiration of cool air. But the most striking -effects proceeded from our power of preserving our natural temperature. -Being now in a situation in which our bodies bore a very different -relation to the surrounding atmosphere from that to which we had been -accustomed, every moment presented a new phenomenon. Whenever we -breathed on a thermometer, the quicksilver sank several degrees. Every -expiration, particularly if made with any degree of violence, gave a -very pleasant impression of coolness to our nostrils, scorched before -by the hot air rushing against them whenever we inspired. In the same -manner our now cold breath agreeably cooled our fingers whenever it -reached them. Upon touching my side, it felt cold like a corpse; and -yet the actual heat of my body, tried under my tongue, and by applying -closely the thermometer to my skin, was 98°, about a degree higher than -its ordinary temperature. When the heat of the air began to approach -the highest degree which this apparatus was capable of producing, our -bodies in the room prevented it from rising any higher; and when it -had been previously raised above that point, invariably sunk it. Every -experiment furnished proofs of this. Mr. Banks and Dr. Solander each -found that his single body was sufficient to sink the quicksilver very -fast, when the room was brought nearly to its maximum of heat. - -495. In a third series of experiments the temperature of the chamber -was raised to the 260th degree. At this time, continues Dr. Blagden, -I went into the room, with the addition to my common clothes of a -pair of thick worsted stockings drawn over my shoes, and reaching -some way above my knees. I also put on a pair of gloves, and held a -cloth constantly between my face and the stove (necessary precautions -against the scorching of the red-hot iron). I remained eight minutes in -this situation, frequently walking about to all the different parts of -the room, but standing still most of the time in the coolest spot near -the lowest thermometer. The air felt very hot, but by no means so as to -give pain. I had no doubt of being able to bear a much greater heat; -and all who went into the room were of the same opinion. I sweated, but -not very profusely. For seven minutes my breathing remained perfectly -good; but after that time, I began to feel an oppression in my lungs, -attended with a sense of anxiety; which gradually increasing for the -space of a minute, I thought it most prudent to end the experiment. -My pulse, counted as soon as I came into the cool air, for the uneasy -feeling rendered me incapable of examining it in the room, beat at -the rate of 144 pulsations in a minute, which is more than double its -ordinary quickness. In the course of this experiment, and others of -the same kind by several of the gentlemen present, some circumstances -occurred to us which had not been remarked before. The heat, as might -have been expected, felt most intense when we were in motion; and on -the same principle, a blast of the heated air from a pair of bellows -was scarcely to be borne: the sensation in both these cases exactly -resembled that felt in our nostrils on inspiration. It was observed -that our breath did not feel cool to our fingers unless held very -near the mouth; at a distance the cooling power of the breath did -not sufficiently compensate the effect of putting the air in motion, -especially when we breathed with force. - -496. On going undressed into the room, the impression of the air was -much more disagreeable than before; but in five or six minutes, a -profuse sweat broke out, which instantly relieved me. During all the -experiments of this day, whenever I tried the heat of my body, the -thermometer always came very nearly to the same point (the ordinary -standard), not even one degree of difference, as in our former -experiments. - -497. To prove that there was no fallacy in the degree of heat shown -by the thermometer, but that the air which we breathed was capable of -producing all the well-known effects of such heat on inanimate matter, -we put some eggs and a beef steak upon a tin frame, placed near the -standard thermometer, and farther distant from the stove than the wall. -In about thirty minutes the eggs were taken out roasted quite hard. In -about forty-seven minutes the steak was not only dressed, but almost -dry. Another beef steak was rather overdone in thirty-three minutes. In -the evening when the heat was still greater, we blew upon a third steak -with the bellows, which produced a visible change on its surface, and -hastened its dressing; the greatest part of it was pretty well done in -thirteen minutes. - -498. The human body, then, may be exposed to a temperature 50° below -zero, without having its own heat appreciably diminished; it may be -exposed to a temperature 60° above that of boiling water, without -having its own heat increased beyond two or three degrees; or, as -appears from experiments subsequently performed expressly to ascertain -this point, from three to five degrees. In the former case, the body -must generate a degree of heat sufficient to compensate the great -quantity of caloric which is every moment abstracted from it by the -intensely-cold surrounding medium. In the latter case it must generate -a degree of cold sufficient to counteract the great quantity of -caloric which is every moment communicated to it by the intensely-hot -surrounding medium. - -499. Powers so wonderful and so opposite appeared to the physiologists -of former times to be involved in such profound mystery, that they -did not even attempt to investigate their nature, or trace their mode -of operation; but satisfied themselves with referring them to some -innate quality of the body, and with considering them as essential -attributes of life. And difficulties connected with the subject still -remain, which the present state of knowledge does not permit us wholly -to surmount; but we are able at least to refer these powers to their -proper seat, and to trace some steps of the processes by which they -produce results so wonderful and beautiful. - -500. It is certain that whatever be the ultimate physical processes by -which the generation of heat and the production of cold are effected -in the animal body, the phenomena are dependent on the condition of -life. No such phenomena take place excepting in living bodies. This is -illustrated in a striking manner by a series of experiments performed -by Mr. Hunter. A part of the living human body was immersed in water -gradually made warmer and warmer from 100° to 118°; precisely the same -part of the body, dead, was immersed in the same water, and both parts, -the living and the dead, were continued in this heat for some minutes. -The dead part raised the thermometer to 114°; the living part raised it -to no higher than 102¼°. On applying the thermometer to the sides of -the living part, the quicksilver immediately fell from 118° to 104°; -on applying it close to the dead part, the thermometer did not fall -above a single degree; the living part actually produced a cold space -of water around it. Hence in bathing in water, whether colder or warmer -than the heat of the body, the water soon acquires the same temperature -with that of the body; and, consequently, in a large bath the patient -should move from place to place, and in a small one there should be a -constant succession of water of the intended heat. - -501. A fresh, that is, a living egg was put into cold water at about -zero, frozen, and then allowed to thaw. By this process its vitality -was destroyed, and consequently its power of resisting cold and heat -lost. This thawed egg was next put into a cold mixture with an egg -newly laid: the time required for freezing the fresh egg was seven -minutes and a half longer than that required for freezing the thawed -egg. - -502. A new-laid egg was put into a cold atmosphere fluctuating between -17° and 15°; it took about half an hour to freeze; but when thawed and -put into an atmosphere at 25° (10° warmer), it froze in half the time. - -503. A fresh egg and one that had been frozen and thawed were put into -a cold mixture at 15°; the thawed one soon came to 32°, and began -to swell and congeal; the fresh one sunk to 29½, and in twenty-five -minutes after the dead one, it rose to 32°, and began to swell and -freeze. - -504. The result of this experiment upon the fresh egg was similar to -that of analogous experiments made upon the frog, eel, snail, &c. where -life allowed the heat to be diminished 2° or 3° below the freezing -point, and then resisted all further decrease; but the powers of life -having been expended by this exertion, the parts then froze like any -other dead animal matter. - -505. The heat of the bird is increased somewhat when it is prepared -for incubation. Some eggs were taken from under a sitting hen whose -temperature was 104°, at the time when the chick was about three-parts -formed. A hole was broken in the shell and the bulb of a thermometer -introduced; the quicksilver rose to 99½°; but in some eggs that were -addled it was proved that their heat was not so high by two degrees, so -that the life of the living egg assisted to support its own temperature. - -506. These facts sufficiently show the dependence of the faculty of -generating heat and of producing cold on the powers of life. But the -processes by which, under the agency and control of the vital powers, -these different results are effected, are various, and even opposite. - -507. The power of generating heat is connected in the closest manner -with the function of respiration, and is directly dependent upon it. -The evidence of this is indubitable. For— - -508. i. Respiration is combustion, and, like ordinary combustion, is -attended with the production of heat. In ordinary combustion oxygen -disappears, and a new compound is formed, consisting of oxygen combined -with the combustible matter; that is, an oxidized body is generated. On -burning a piece of iron wire in oxygen, the oxygen disappears, and the -iron increases in weight. The oxygen combines with the iron, forming -a new product, oxide of iron, and the weight of this new substance -is found on examination to be exactly equal to the weight of the -wire originally employed, added to the quantity of oxygen which has -disappeared. - -509. It is precisely the same in respiration. In this process oxygen -combines with combustible matter, carbon: the oxygen disappears, and a -new body, carbonic acid, is generated. - -510. ii. One phenomenon which invariably accompanies the combination of -oxygen with combustible matter is the extrication of heat. Whenever a -substance passes from a rarer into a denser state; when, for example, a -gas is converted into a liquid or solid, or when a liquid solidifies, -heat is evolved; because, according to the ordinary theory of -combustion, the denser substance has a less capacity for caloric than -the rarer, and consequently in passing from a rare into a dense state, -a quantity of caloric previously combined or latent within it is set -free. The combined or latent caloric contained in a body is termed its -specific caloric; the caloric which is evolved on its change of state -is named free or sensible caloric. - -511. The combination of oxygen with carbon, as in the combination -of oxygen with combustible matter in every other instance, must -be attended with the evolution of heat. Though the product of the -combustion, in the present case, be a gaseous body, carbonic acid, -still, according to the ordinary theory of combustion, carbonic -acid has less specific caloric, or less capacity for caloric, than -oxygen; and therefore in combining with carbon, a portion of its -specific caloric becomes free or sensible, that is, heat is evolved. -But whatever theory of combustion be adopted, the fact is certain, -that whenever oxygen combines with carbon to form carbonic acid, -heat is evolved; not only in the rapid union which takes place in -ordinary combustion, but also in the slow combination which occurs in -fermentation, putrefaction, and germination; in the latter of which -processes, as in the malting of barley, the temperature rises as high -as 10°. The union of oxygen with carbon in the lungs during respiration -must therefore necessarily produce heat, just as it does in a charcoal -fire, or in any other natural process in which this combination takes -place. - -512. iii. Numerous phenomena connected with the animal body show that -its temperature is in strict proportion to the quantity of oxygen which -is consumed in respiration, and to the quantity of carbonic acid which -is formed by the union of oxygen and carbon during the process. - -513. In all animals whose respiratory organs are so constructed, that -the consumption of oxygen and the consequent generation of carbonic -acid is minute in quantity, the production of heat is proportionably -small. It has been shown (337 _et seq._), that in almost the entire -class of the invertebrata, the respiratory apparatus is comparatively -minute and imperfect; accordingly, in these animals the power of -generating heat is at the minimum. In the fish, though the respiratory -apparatus be large, and though all the blood of the body circulate -through it (345 _et seq._), yet only a small quantity of air is brought -into contact with the respiratory organ, merely the air contained in -water. In the reptile, though it possess a true and proper lung, and -respire air, yet only one half of the blood of its body circulates -through the comparatively small, imperfectly divided, and simply -constructed air bag, which constitutes its respiratory organ (354). -Hence, the striking contrast exhibited between the temperature of these -cold-blooded creatures and that of the mammiferous quadruped, whose -lung, comparatively large, and composed of innumerable minute and -closely-set air vesicles (fig. CXXXIV. and CXXXV.), presents to the air -an immense extent of surface (370), and the whole mass of whose blood -incessantly traversing this surface, comes at every point into contact -with the air (399). - -514. In the various tribes of warm-blooded animals, the elevation -and uniformity of the temperature is strictly proportionate to the -comparative magnitude of the lungs; to the complexity of their -structure; to the minuteness and number of the air vesicles; and, -consequently, to the quantity of oxygen consumed, and of carbonic acid -generated. - -515. In all animals with red blood there is a strict relation between -the temperature of the body and the lightness or depth of the colour -of the blood; invariably the deeper the colour, the higher the -temperature. Thus, the blood of the fish and of the reptile is of a -light, and that of the bird of an intense red colour. It has been shown -(229) that the lightness or deepness of the colour of the blood depends -on the quantity of red particles which it contains, and the chemical -action between the air and the blood is carried on chiefly through the -medium of the red particles. - -516. Even in the same animal, the temperature differs at different -times, according to the energy with which the process of respiration -is carried on. When the circulation of the blood is sluggish and the -respiration slow and feeble, the quantity of oxygen consumed is small, -and the temperature low; when, on the contrary, the circulation is -rapid, and the respiration energetic, the quantity of oxygen consumed -is large, and the temperature proportionably high. Whatever diminishes -the quantity of air that flows to the lungs, and the quantity of blood -that circulates through them, diminishes the temperature. Malformation -of the heart, in consequence of which a quantity of blood is sent to -the system without passing through the lungs, as in the individuals -termed Ceruleans: disease of the lungs, by which the access of air -to the air vesicles is obstructed, as in asthma, are morbid states -invariably attended with a diminution of the temperature. - -517. When a warm-blooded animal is placed in an elevated temperature, -its consumption of oxygen is comparatively small; when it is placed -in a cold atmosphere, and the production of a large quantity of heat -is necessary to maintain its temperature at its natural standard, its -consumption of oxygen is proportionably large; accordingly, it is -established by direct experiment that the same animal consumes a much -larger quantity of oxygen in winter than in summer. - -518. Due allowance being made for the difference in their bulk, young -animals consume less oxygen than adults; and they have a less power of -generating heat. Different species of young animals differ from each -other in their power of generating heat, and the closest relation is -observable between the difference in their power of consuming oxygen -and that of generating heat. Puppies and kittens require so small -a quantity of oxygen for supporting life, that they may be wholly -deprived of this gas for twenty minutes, without material injury, while -adult animals of the same species perish when deprived of it only for -four minutes. As long as these young creatures retain the power of -sustaining life for so protracted a period without oxygen, they are -wholly incapable of maintaining their own temperature; on free exposure -to air, even in summer, the heat of their body sinks rapidly, and if -this exposure be continued long, they perish of cold. In like manner, -young sparrows and other birds which are naked when hatched, consume -little oxygen, and are incapable of maintaining their temperature; but -can support life when deprived of oxygen much longer than adult birds -of the same species; while young partridges which are able to retain -their own temperature at the period of quitting the shell, die when -deprived of oxygen as rapidly as the adult bird. - -519. The state of hybernation illustrates in the same striking manner -the relation between respiration and the generation of heat. One of the -most remarkable phenomena connected with this curious state, is the -reduction, sometimes even the apparent suspension, of respiration; and -in all cases of hybernation, the respiratory function is performed in -a feeble manner, and only at distant intervals. Exactly in proportion -to the diminution of the respiration, is the reduction of the power of -generating heat; so that when the state of hybernation is established, -the temperature of the external parts of the body sinks nearly to that -of the surrounding medium; while the internal parts, the blood, and -the vital organs are only a degree or two higher. In experiments made -to reduce an hybernating animal to a torpid state by cold artificially -produced, De Saissy found that he could not bring on the state of -hybernation by the reduction of temperature alone, without also -constraining the respiration. - -520. These and other analogous facts abundantly establish the relation -between the function of respiration and that of calorification, and -lead to the general conclusion that the generation of animal heat is -in the direct ratio of the quantity of air and blood which are brought -into contact, and which act on each other in a given time. Yet an -attempt has recently been made by an ingenious physiologist[3] to -disturb this induction, and to show that the production of animal heat -is not in the direct ratio of the quantity of oxygen inhaled, but in -the inverse ratio of the quantity of blood exposed to this principle. -This position is maintained on the following grounds:— - - [3] An Experimental Inquiry into the Laws which regulate the Phenomena - of Organic and Animal Life. By George Calvert Holland, M.D. and more - complete than the expirations; it is a state of continual sighing. In - like manner, in certain diseases, such as asthma, the inspirations - greatly preponderate both in frequency and energy over the - expirations. In such conditions of the system the blood accumulates - in preternatural quantity in all the internal organs; but more - especially in the lungs; and two consequences follow: first, there - is a remarkable diminution in the energy of all the vital actions; - and secondly there is a proportionate diminution in the production of - animal heat. - -521. Inspiration favours the flow of blood to the lungs; expiration -retards it: consequently, if from any causes the inspirations -preponderate in number and proportion over the expirations, a greater -quantity of blood than usual will be accumulated in the lungs. There -are conditions of the system in which this preponderance of the -inspirations actually takes place; when the mind is under the influence -of certain emotions, for example, as when it is depressed by anxiety -and fear. In this state the inspirations are more frequent - -522. On the contrary, as it is the effect of inspiration to facilitate -the motion of the blood through the lungs, so it is the effect of -expiration to retard it; hence, when the expirations preponderate the -opposite state of the system is induced; all the vital actions are -performed with increased energy; the heart beats with unusual vigor; -the pulse becomes quick and strong; a larger quantity of blood is -determined to the surface of the body, and this excited state of the -system is always attended with an augmentation of the temperature. - -523. As in the first state there is a greater and in the second a -smaller quantity of blood than natural contained in the lungs, the -inference deduced by Dr. Holland is, that the production of animal heat -is in the inverse ratio of the quantity of blood exposed to oxygen. But -this inference is neither logical nor sound. - -524. If, as a comparison of all the phenomena of respiration exhibited -throughout the entire range of the animal kingdom, shows the production -of animal heat to be in the direct ratio of the quantities of air and -blood which are brought into contact, and which re-act on each other, -every phenomenon of respiration must be in harmony with this law, and, -accordingly, when really understood, it is found to be so. - -525. Inspiration, by the dilatation of the thorax, and consequently of -the lungs incident to that action, is favorable to the flow of blood to -the lungs. But it is only a certain degree of dilatation of the lungs -that is favorable to the flow of blood through them (407 _et seq._). -If the dilatation be carried beyond a certain point, the quantity of -blood transmitted through the pulmonary tissue is diminished (406); -if the dilatation be carried farther, the transmission of the blood -may be wholly stopped (417). The quantity of the blood which flows to -the lungs, and the quantity which circulates through them, are not -then identical. So large a quantity may flow to them as to impede or -retard or wholly stop the pulmonary circulation. In proportion to the -accumulation of blood in the lung must necessarily be the distension of -the pulmonary tissue; in that proportion the lung must be approximated -to its condition in the experiment in which it was distended with water -(417), when it did not transmit a single particle of blood. Further, -in proportion to the preternatural distension of the pulmonary tissue -with blood must be the exclusion of air from the air vesicles for the -lungs can contain only a certain quantity of blood and air (418.3), so -that the blood can preponderate only by the exclusion of the air. - -526. In those states of the system, then, in which the preponderance -of the inspirations induces a preternatural accumulation of blood in -the lungs, the production of animal heat is diminished for a two-fold -reason; first, because the distension of the pulmonary tissue with -blood retards the pulmonary circulation, and proportionally lessens -the quantity of blood which is brought into contact with the air; -and, secondly, because the distended blood-vessels compress the air -vesicles, and so diminish the quantity of air which is brought into -contact with the blood. - -527. It follows that the diminution of temperature which takes place in -this condition of the system is not because the production of animal -heat is in the inverse ratio of the quantity of blood which is exposed -to oxygen; but because from a two-fold operation there is a diminution -of the quantity of blood and of oxygen which are brought into contact. - -528. The reason is equally obvious why there is an increase of -the temperature in those conditions of the system in which the -expirations preponderate over the inspirations. Expiration, it is -true, somewhat retards the circulation of the blood through the lungs, -but the preponderance of this respiratory action does not raise the -temperature by the retardation of the flow of blood through the lungs, -and the consequent diminution of the quantity transmitted in a given -time; for though expiration somewhat retards the circulation of the -blood through the branches of the pulmonary artery, it promotes its -circulation through the branches of the pulmonary veins (fig. CXL. 10). -It is indeed by the action of expiration that the aërated blood is -transmitted from the lungs to the left heart to be sent out renovated -to the system. Expiration has no influence whatever over the aëration -of the blood. Before the action of expiration takes place, the blood -is already aërated. The office of expiration is to remove from the -system the air which has served for respiration, and to transmit to the -system the blood which has been subjected to respiration. Consequently, -in those states of the system in which the expirations preponderate, -the temperature is increased, not because the expiratory actions, by -lessening the quantity of blood in the lungs, diminish the quantity -exposed to oxygen, but because they transmit to the system oxygenated -blood as rapidly as it is formed, that is, blood which either produces -animal heat in the act of its formation, or which generates it as it -flows through the system. - -529. These conditions establish the conclusion deduced, as has -been stated, from the comparison of the phenomena of respiration -exhibited throughout the entire range of the animal kingdom. But if -the production of animal heat be really the result of combustion, -if that combustion take place in the lung, and if the lung be thus -the focus whence the heat radiates to every other part of the body, -why is not the heat of this organ and of the parts in its immediate -neighbourhood higher than the temperature of the rest of the body? -Some of the internal organs are indeed a degree or two hotter than the -general mass of the circulating blood (469), and among these the lung -is admitted to rank perhaps the very highest. But how can a quantity of -caloric sufficient to maintain the heat of the body in a temperature -of forty degrees below zero radiate from an organ the temperature of -which is only two or three degrees above that of the body itself? It -is estimated that, in every minute, during the calm respiration of a -healthy man of ordinary stature, 26·6 cubic inches of carbonic acid, -at the temperature of 50° Fahr. are emitted, and that an equal volume -of oxygen is withdrawn from the atmosphere. From these data it is -calculated that, in an interval of twenty-four hours, not less than -eleven ounces of carbon are consumed. Why is the lung, the seat of this -combustion, not only not greatly warmer than any other organ; but why -is it not even consumed by the fire which is thus incessantly burning -within it? - -530. It has been shown (468 and 469) that when the carbon of the -blood unites in the lung with the oxygen of the air, the nature of -the blood, in consequence of the abstraction of carbon, undergoes an -essential change, passing from venous into arterial. By an elaborate -series of experiments, conducted with extraordinary care and skill, -it would appear that arterial has a greater capacity for caloric than -venous blood, in the proportion of 114·5 to 100. In consequence of this -difference in the constitution of the two kinds of blood, the heat -generated in the lung by the combustion of carbon, instead of being -evolved or becoming sensible (510. ii.), and so raising the temperature -of the organ, goes to satisfy the increased capacity for caloric of -arterial blood, is spent, not in rendering the fluid sensibly warmer, -but in augmenting its specific caloric (510. ii.). Arterial blood is -not increased in temperature,[4] but with its absolute quantity of -caloric augmented, flows from the lung to the left heart (fig. CXL. -10), and thence to the system (fig. CXL. 6). In the system, in every -organ, at every point of the component tissue of every organ and at -every moment of time, the blood repasses from the arterial to the -venous state: by this transition its capacity for heat is diminished; -the venous cannot retain in it the same quantity of caloric as the -arterial blood, consequently a portion of caloric is extricated; that -which was latent becomes sensible, and caloric being set free the -temperature is raised. In this process the lung is not burnt, it is -only rendered just sensibly warmer than any other part of the body, -though it be the organ by which the whole mass of blood receives its -caloric, because it is only in the capillary part of the systemic -circulation, when the arterial blood again passes into the venous -state, that the caloric acquired is liberated. In this manner, gently, -steadily, uninterruptedly, an abundant, unceasing, and equable current -of heat is distributed to every part and particle of the system. - - [4] It is not a perfectly accurate statement that the temperature of - venous and arterial blood is precisely the same. The latest and best - experiments concur in showing that arterial blood, at least in the - heart and the great arterial trunks, is one or two degrees warmer than - venous blood. The weight of evidence from experiment is also in favour - of the opinion, that the different parts of the body are _somewhat_ - less warm as they recede from the lungs and heart; but the difference - is so slight that it may be disregarded in the general argument. - -531. Such is the celebrated theory of animal heat suggested by Dr. -Crawford, of which it has been justly said, that it affords one of the -most beautiful specimens of the application of physical and chemical -reasoning to the animal economy that has ever been presented to the -world. - -532. The main position on which this theory rests—that arterial -possesses a greater capacity for caloric than venous blood—professes -to be founded on experiments which, though of a delicate and complex -nature, are nevertheless uniform and decisive in their results. -In consequence of their extreme interest and importance, these -experiments have been subjected, by different physiologists, to rigid -examination, with a somewhat conflicting result. The greater number -of experimentalists maintain that Crawford’s experiments are correct -in all the essential points, and that the objections which have been -urged against them do not really affect them; while others are of -opinion that, even although it must, upon the whole, be admitted that -the specific heat of arterial is greater than that of venous blood; -yet that the excess is so small as to be inadequate to account for -the effects attributed to it. Dr. Davy’s experiments, which of all -that have been instituted are generally conceived to be the most -unfavourable to the theory of Crawford, do not afford uniform results. -Three experiments out of four indicate a greater capacity in arterial -than in venous blood; in those in which the experimentalist himself -places the most confidence, in the relative proportion of 913 to 903; -while, according to Crawford, the relative proportion is 114·5 to 100. - -533. But when this subject is closely considered, the discrepancy -in question turns out to be of no real consequence. There is a -modification of the theory, which removes every difficulty, and -dispenses with the necessity of any regard whatever to the point in -dispute. - -534. It has been shown (444 _et seq._), that during the process of -respiration more oxygen disappears than is accounted for by the -carbonic acid that is generated; that this excess of oxygen is absorbed -by the blood; and that in the lung the oxygen merely enters into a -state of loose combination with the blood, the union being intimate -and complete only in the system. The complete chemical combination -of the oxygen with the carbon takes place, then, not in the lungs, -but in the capillary arteries of the system; consequently it is only -while flowing in capillary arteries that carbonic acid is formed; that -is, it is only in these vessels that the arterial combustion takes -place: of course, therefore, it is only in these vessels that heat -is extricated, and only from them that it can be communicated to the -adjacent parts. According to this view, wherever there is a capillary -artery, the combustion of carbon incessantly goes on, and there caloric -is as incessantly set free; but since there is not a point of any -tissue, in which there are not capillary arteries, there is not a point -from which caloric does not radiate. As soon as formed, carbonic acid -passes from the capillary arteries into the capillary veins; by the -veins it is transmitted to the lungs; and by the lungs it is expelled -from the system. The real operations carried on in the lungs, then, -are the transmission of oxygen and the extrication of carbonic acid; -but this organ is not the seat of the essential and ultimate part -of the function; it is merely the portal through which the elements -employed in the process have their entrance and exit. Thus the question -concerning the greater capacity of arterial blood for caloric is of -no importance whatever: the phenomena may be equally accounted for, -whatever be, in this respect, the constitution of the blood. - -535. The result of the whole is, the complete establishment of the -fact, that the production of heat in the animal body is a chemical -operation, dependent on the combination of oxygen with carbon in the -capillary arteries of the system; that is, it is the result of the -burning of charcoal at every point of the body. - -536. The agent which maintains and regulates this internal fire is the -nervous system. There is, indeed, reason to suppose that the nervous -system, in some mode or other, contributes to the actual production -of animal heat. It is established by direct experiment, that the -quantity of carbonic acid formed in the system is inadequate to the -supply of the caloric expended by it; that in a given time more heat -is abstracted from the body by the surrounding medium, than can be -accounted for by the consumption of the amount of carbonic acid thrown -off by the lungs during the same interval. There is evidence that the -source of this additional heat is the nervous system. - -537. The influence exerted by the nervous system over the production -of animal heat, is demonstrated by the fact, established by numerous -observations and experiments, that whatever weakens the nervous power, -proportionally diminishes the capacity of producing heat. For, - -1. The destruction of a portion of the spinal cord diminishes the -temperature of an animal without, as far as is ascertained, the -disturbance of any other function. - -2. The privation of the heart and blood-vessels of the nervous -influence, as by decapitation, though the passage of the blood through -the lungs and its ordinary change from the venous to the arterial state -be maintained by artificial respiration, greatly diminishes, if it do -not altogether suspend, the generation of animal heat. - -3. The abolition of sensibility by the administration of a narcotic -poison, artificial respiration being maintained, as effectually -disturbs the generation of animal heat as decapitation; while the power -of generating heat is restored, in the exact proportion to the return -of the sensibility by the cessation of the action of the poison. - -4. The temperature of an organ is found, by direct experiment, to be -diminished by the division of the nerves that supply it with nervous -influence. The nerves that supply the horn were divided on one side -of the body in a young deer; the other horn was left entire. The -temperature of the horn—the nerves of which had been divided—was -found, after some hours, to be considerably diminished, and it -continued diminished for several days; at length its temperature was -restored. On examining the horn about ten days after the operation -had been performed, the divided nerves were found to be connected by -a newly-formed substance; thus apparently accounting for the loss of -temperature in the first instance, and for its subsequent restoration. - -538. But although these and other analogous facts prove, beyond all -question, the important influence of the nervous system over the -development of animal heat, yet the mode in which that influence -operates is not ascertained. Its action may be either direct or -indirect. The nerves may possess some specific power of generating -heat,—extricating it immediately from the blood by a process analogous -to secretion,—or they may evolve it indirectly by other operations, as -by some of the processes of nutrition. Each hypothesis is maintained -by able physiologists; but the balance of evidence (as will appear -hereafter) is greatly in favour of the opinion that the influence -of the nervous system over this process is altogether indirect. A -beautiful illustration of this is afforded in the following operation, -which is going on, without ceasing, every instant during life. - -539. The skin which forms the external covering of the body is composed -essentially of gelatin. No gelatin is contained in the blood; but the -albumen of the blood is capable of being converted into gelatin by the -addition of oxygen. Albumen is received by the capillary artery of the -skin; the blood, of which albumen forms so important a constituent, -contains a quantity of oxygen which it receives at the moment of -inspiration, and which it retains in a state of loose combination -(470 _et seq._). Under the influence probably of the organic nerve, -the capillary artery chemically combines a portion of the free oxygen -with the albumen of the blood, and gelatin is the result. In this -process the albumen gives off carbon; the blood affords oxygen; the -two elements unite; carbonic acid is formed; and, as in every other -instance in which carbonic acid is formed, heat is evolved. In this -manner a fire is kindled, and is kept constantly burning, where it -is most needed to counteract the influence of external cold, at the -external surface of the body. - -540. Such are the main points which have been established in relation -to the production and distribution of animal heat. But it has been -shown that the living body is capable of bearing without injury a -temperature by which it is rapidly consumed when deprived of life. By -what means does the vital power enable the body to resist the influence -of such intense degrees of heat? - -541. Two circumstances are observable when the body is placed in a -temperature greatly higher than its own. First, it can endure such -a temperature only in the medium of air. Air can easily be borne at -the temperature of 260°; aqueous vapour at the temperature of 130° -few Europeans are capable of enduring longer than twelve minutes; the -peasants of Finland appear to be able to sustain it, for the space of -half an hour, as high as 167°; but the hottest liquid water-bath which -any one seems to have been able to bear for the space of ten minutes, -is the hottest spring at Barêges, the temperature of which is 113°. -But in heated air the quantity of heat in actual contact with the body -is much less than in the other media; because in proportion as the -air is heated it is expanded, and in proportion as it is expanded the -particles are diminished that come into contact with the body. - -542. In the second place, the afflux of the colder fluids from the -central parts of the system to the surface may for a time exert some -influence in keeping down the temperature of the body. But above all -this, in the third place, a two-fold provision is made in the body -itself for the reduction of its temperature when exposed to intense -degrees of heat; by the one, the power with which it is endowed -of producing heat is diminished; by the other, cold is positively -generated. - -543. It has been shown (517) that in proportion to the elevation -of the temperature to which the body is exposed the blood becomes -less venalized, and in the proportion in which the blood retains its -arterial character the consumption of oxygen is diminished. Venous -blood contains an excess of carbon, arterial blood an excess of oxygen. -Consequently in proportion as the blood retains its arterial character -it affords less carbon for the combination of oxygen, that is less -inflammable matter. At an elevated temperature therefore there must, of -necessity, be a diminished production of heat within the body, since -the blood contains a diminished quantity of combustible material. - -544. Moreover, in proportion to the elevation of the temperature to -which the body is exposed, evaporation takes place from the entire -surface of the pulmonary vesicles. No experiments have been performed -which enable the physiologist to ascertain precisely the quantity of -vapour exhaled from the lungs in a given time, when the body is exposed -to a given degree of heat; but both observation and experiment show -that it is very great. The blood pours out upon the whole surface of -the air vesicles a quantity of moisture in the form of water: by the -surrounding air this water is converted into vapour: by the conversion -of a fluid from the state of a liquid into that of vapour caloric is -absorbed: by the absorption of caloric cold is generated, and that to -such a degree that fluids exposed to the influence of evaporation may -be frozen in the intensest heat of summer. The very process by which -art, aided by science, affords to the inhabitants of warm climates the -luxury of ice, is that by which nature generates cold in the human -lungs when the body is exposed to a temperature above its own. Not -only, then, is the lung the instrument by which the body acquires the -power of evolving heat in greater or less quantity in proportion to -the demands of the system, but this very same organ, under a change -of circumstances, produces the directly contrary effect, and actually -generates cold. - -545. In the process of producing cold the skin is a powerful auxiliary -to the lungs. More fluid is, indeed, evaporated from the surface of the -skin in the form of perspiration, than from the lungs in the form of -vapour; the cutaneous, like the pulmonary evaporation, increases in the -ratio of the temperature, and both co-operate in abstracting the excess -of caloric. - -546. Finally, in proportion to the elevation of the temperature is -the acceleration of the circulation; the pulse is augmented in power, -and doubled or trebled in frequency (495); but in proportion to -the rapidity of the circulation is the increase of the quantity of -evaporable matter which is transmitted to the evaporating surfaces. - -547. From the whole it appears that by the combination of carbon and -oxygen provision is made for the production of the greatest quantity -of caloric that can at any time be required for the wants of the -system; that when a decreased evolution of heat is necessary a smaller -quantity of carbon and oxygen is brought into union, and that when, -from exposure to intense degrees of heat, it is requisite for the -maintenance of the temperature of the body at its own standard, that -it should actually generate cold, it accomplishes this object by the -evaporation of water. - - - - -CHAPTER X. - -OF THE FUNCTION OF DIGESTION. - - Process of Assimilation in the plant; in the animal—Digestive - apparatus in the lower classes of animals; in the higher - classes; in man—Digestive processes—Prehension, Mastication, - Insalivation, Deglutition, Chymification, Chylification, Absorption, - Fecation—Structure and action of the organs by which these operations - are performed—Ultimate results—Powers by which those results are - accomplished—Two kinds of digestion, a lower and a higher; the former - preparatory to the latter. - - -548. Digestion is the function by which the aliment is converted into -nutriment. No food can nourish until it be converted into a fluid -analogous in chemical composition to that of the body by which it is -assimilated. The conversion of the crude aliment into such a fluid is -effected by a vital power peculiar to living beings, by which they -subvert the constitution of other organized bodies, and cause them to -assume their own. They accomplish this change by the agency of certain -secretions which they elaborate in their own organs, and which they -add to the substances they receive as aliment. By the action of these -secretions, the chemical composition of the aliment is brought into a -close affinity to that of the body which it nourishes. - -549. This change in the chemical composition of the aliment, by means -of fluids secreted by the living bodies which receive it, is manifest -in the plant as well as in the animal. The sap, as it issues from the -root, is a colourless and limpid fluid; it has a specific gravity -a little greater than that of water; it has a sweetish taste; it -contains an acid which is sometimes free, and is either the carbonic -or the acetic; but more commonly it is combined with lime or potass. -To this crude sap, in this the first stage of its formation, vegetable -secretions, sugar and mucus, assimilative substances, are superadded, -probably by the fibres of the root. - -550. As the sap ascends in the stalk, a greater quantity and a greater -number of these vegetable secretions are poured into it. In the ratio -of its elevation it acquires sugar, mucus, albumen, and an azotized -substance analogous to gluten. By the admixture of these assimilative -secretions, the crude sap is progressively assimilated nearer and -nearer to the chemical composition of the proper nutritive fluid of the -plant. Thus prepared, the sap passes to the leaf, in the upper surface -of which it undergoes a process analogous to that of digestion in the -animal (315), and is converted into proper nutrient matter. - -551. The plant can only take up, by absorption, liquid food; it never -receives solid substances as aliment: it therefore needs no apparatus -for the division, solution, and fluidification of its food; its sole -work of assimilation consists in changing the innate affinities -of liquid aliment. But animals which live on vegetable and animal -substances have to modify, by their digestive juices, the affinities of -organic solids: hence assimilation in the animal must necessarily be a -more complex operation than it is in the plant. - -552. Fixed immovably to the soil by its roots, the nutritive apparatus -of the plant is always in contact with its food, which is slowly but -unceasingly absorbed according to the wants of its system. But the -animal endowed with the faculty of locomotion receives its aliment into -the interior of its body, that it may transport its food along with it -in all its changes of place; and that, as in the plant, its food may be -always in contact with its nutritive apparatus. The interior nutrition -of the animal and the convergence of its nutritive apparatus to the -centre of its system, and the exterior nutrition of the plant and the -divergence of its nutritive apparatus to the peripheral extremity of -its body, are differences in their mode of nutrition, connected with -essential differences in the mode of life peculiar to the two beings. - -553. Plant-like animals have a plant-like mode of nutrition. The -transition from the one class to the other is so gradual as to be -almost insensible. Fixed to the same spot in the ocean as the tree to -the land, the nutritive surface of the poriferous animal is always in -contact with the water, as the soil is with the external surface of -the plant. The cellular substance of which the bag of the poriferous -animal is composed is permeated in all directions by ramifying and -anastomosing canals, which, beginning by minute pores placed on the -external surface, terminate in larger orifices, termed vents, which -are fecal openings. These internal canals are incessantly traversed by -streams of water, which enter through the minute, and are discharged -through the larger orifices. By these currents the nutrient matter -contained in the water is conveyed to every part of the body, and -the streams that issue from the fecal orifices abound with minute -flocculent particles, the residue of the digested matter. No separate -part of the body is appropriated to the function of digestion any -more than in the plant; there is merely a general absorbent surface; -the water is to this animal what the soil is to the plant; its whole -surface is a root; every point of that surface is constantly in contact -with its food, and every point is absorbent. - -554. In the class above the porifera, the margins of the superficial -pores are merely lengthened out into minute sacs, irritable and -sentient, surrounded with vibratile cilia (342). These sacs, which are -termed polypi, are so many little stomachs, which select, seize, and -digest the food brought to them in the currents of water created by the -action of the cilia (344). - -[Illustration: Fig. CXLVIII.—_Hydra Viridis._ - - 1. The Hydra with its tentacula expanded. 2. The tentacula. 3. The - body of the Hydra. 4. Disc for attachment. 5. The Hydra in the act of - creeping. 6. The Hydra with an animalcule in its digestive cavity.] - -555. The fresh-water polype, the little hydra (fig. CXLVIII. 1), is one -of these minute sacs detached and endowed with the power of locomotion -(fig. CXLVIII. 5), a sentient, self-moving digestive bag. Capable of -swallowing animals many times its own size, as the red-blooded worm, -this little creature stretches its whole body like a thin elastic -membrane over its prey, so as completely to alter its own shape, and -the membranous substance of which it is composed becoming transparent -by the distention, allows the subsequent process to be distinctly seen. -The red fluid of the worm, as the process of digestion advances, is -slowly diffused over every part of the internal surface of the polype. -The whole internal surface of this minute self-moving bag is digestive; -a true and proper stomach (fig. CXLVIII. 6). By dexterous manipulation, -this internal surface may be rendered external, and the animal turned -completely inside out. Then the external begins to perform the office -of the internal surface, carrying on the function of digestion, -just as well as that which was primitively formed for it; while the -originally digestive becomes the generative surface, for the creature -buds from this surface, now the outer one; a striking and instructive -illustration of the analogy between the external covering of the animal -body or the skin, and its internal lining, or the mucous surface. - -[Illustration: Fig. CXLIX. - - Group of Monades; the dark spots in the interior of their bodies - representing their digestive sacs.] - -556. In the monades (fig. CXLIX.), and in all the lower animalcules, -the digestive apparatus, instead of forming the entire internal -surface of the body, consists of numerous sacs, which constitute so -many separate stomachs, whence the name of the class, _polygastrica_. -When empty, or when filled with water, these digestive sacs cannot -be distinguished from the common cellular tissue of the body; but on -feeding the animals with coloured organic matter, minutely diffused in -water, the coloured particles readily enter the digestive sacs, and -render apparent their form and arrangement. In the minutest animal -hitherto appreciable, the monas termo, the 2000th part of a line -in diameter, four rounded sacs have been seen filled with coloured -particles (fig. CXLIX.). Each of these sacs, about the 6000th part of -a line in diameter, opens by a narrow neck into a funnel-shaped mouth, -surrounded with a single row of long vibratite cilia, by the action -of which the floating organic particles are brought within the reach -of the mouth. In general, even in this class, an alimentary canal -traverses the whole extent of the body, into which all the different -stomachs open. Sometimes numerous branches proceed from the main trunks -of the alimentary canal, bearing the nutritive matter to the different -parts of the body (fig. CL. 2). Often, in order to extend the digestive -surface, the alimentary canal is produced, forming rounded enlargements -called cœcal appendages, all of which act as so many additional -stomachs (fig. CLI. 3). In some individuals, observed under favourable -circumstances, nearly 200 of these cœcal stomachs, filled with coloured -matter, have been counted, and there may have been many more unseen, -because empty and collapsed. In the lowest tribes of this class -there is but one orifice to the alimentary canal, the oral; the food -entering, and the fecal matter passing out of the system by the same -aperture; but in the higher orders there is both an oral and an anal -orifice, and the mouth and the anus are placed at opposite extremities -of the body, as in the higher animals. - -[Illustration: Fig. CL.—_Fasciola Hepatica._ - - 1. Mouth. 2. Alimentary tubes. 3. Sucker.] - -557. Up to this point in the animal series the digestive sacs and the -alimentary canal are merely cavities formed in the common cellular -tissue of the body, without any lining membrane, without teeth, or -without any instruments for dividing and preparing the aliment, and -without a single gland, as far as has been ascertained, to assist the -digestive process. All the assimilative functions, the respiratory as -well as the digestive, appear to be performed by this single surface. -But in the ascending scale not only is an apparatus appropriated to -digestion, perfectly distinct from that assigned to respiration, -but even the stomach and the alimentary canal are separate organs, -distinguished from each other, both in structure and function. -Still higher in the scale new organs are successively added, as the -process becomes more complex and refined, in order to assist the main -operations carried on in particular parts of the apparatus; and as -that apparatus approaches its highest degree of perfection, not only -do the several parts of which it is composed increase in number and -complexity, but each part becomes more and more isolated from the rest, -a specific office being assigned to each in the division of labour -that is made. Viewing, however, the digestive apparatus as a whole, -whether simple or complex, whether consisting of a single uninterrupted -surface, or divided into many separate portions, its nature is -universally and invariably the same, and from the monad to man is -endowed with analogous vital energies. - -[Illustration: Fig. CLI.—_Aphrodita Aculeata._ - - 1. Proboscis in a retracted state. 2. Interior of digestive cavity. - 3, 3. Cœcal appendages opening into it.] - -558. Comparative anatomy, which has succeeded in tracing through the -different classes, orders, genera, and countless tribes of animals, -the modifications in form and structure of the digestive apparatus, -has shown that those modifications are invariably in strict adaptation -to the kind of food on which the apparatus is destined to act and to -the extent of the elaboration requisite to convert crude aliment into -proper animal substance. To trace this adaptation through the rising -and ever-varying series, is a most interesting and instructive study, -not only exhibiting, in the very organs that elaborate its food, the -physical and even the mental qualities assigned by the hand of nature -to each individual, but oftentimes shedding a clear and bright light on -the complex structures of the highest and most perfect organization. -Striking and beautiful illustrations are afforded by these -investigations of the principle formerly insisted on (vol. i. chap. i. -p. 28, 3), that the communication of the higher faculties exalts the -apparatus even of the very lowest processes, that the latter may work -in harmony with the former. In conformity with this principle, as the -nobler endowments exalt the animal in the scale of organization, so -even its very digestive apparatus becomes extended, isolated, complex -and refined. - -559. The highest and most perfect form of the digestive apparatus is -that which is disposed in a series of chambers in free communication -with each other. In these chambers the food undergoes a succession of -changes, by which it is progressively assimilated to the nature of -animal substance. This assimilation, however, is never effected by the -sole agency of the chambers themselves; it is accomplished, to a great -extent, by the influence of special organs placed in the neighbourhood -of the digestive chambers. In the lowest animal there is but one -substance and one surface for every function; in the highest, even for -the performance of the lowest function, there is the combination of -many substances which are arranged in complex modes. - -560. In man, the digestive chambers are five; the auxiliary organs are -many. - -The first of these chambers is the cavity called the mouth; the -second is the bag termed the pharynx; the pharynx communicates by the -esophagus with the third chamber, the stomach; the fourth chamber -consists of the convoluted tubes named the small intestines, and the -fifth consists of the larger tubes, denominated the large intestines. -The assistant organs are, first, numerous appendages to the mouth, -namely, the tongue, the teeth, the salivary glands, and the muscles -that work the jaws; and, secondly, certain appendages to the small -intestines, namely, the pancreas, the liver, the mesenteric glands, and -the lacteal vessels. - -561. By the mouth the food is softened and reduced to a pulp; by the -tongue, materially aided by the soft palate, this pulp, when duly -prepared, is transmitted to the pharynx; received by the pharynx, it -is sent on to the esophagus; by the esophagus, it is conveyed to the -stomach; in the stomach, it is converted into a peculiar substance -called chyme; the chyme, passing from the stomach into the first -portion of the small intestines, is there converted into the substance -called chyle; the chyle, carried slowly along the remaining portion of -the small intestines, is successively absorbed by the lacteals; by the -lacteals, it is conveyed through the mesenteric glands to the thoracic -duct, and by the thoracic duct it is poured into the venous blood close -to the heart. By the large intestines the refuse matter is conveyed out -of the system. - -562. The function of digestion consists, then, of the following -processes:— - -1. Prehension. 2. Mastication. 3. Insalivation. 4. Deglutition. -5. Chymification. 6. Chylification. 7. Absorption. 8. Fecation. - -563. Prehension is the reception of the aliment; mastication is the -mechanical comminution of it; insalivation is the admixture of it with -certain juices poured into the mouth; deglutition is the transmission -of it, when duly moistened and divided, into the stomach; chymification -is the conversion of it into chyme; chylification is the conversion of -the chyme into chyle; absorption is the assumption of the chyle by the -lacteals and the transmission of it into the blood, and fecation is -the separation and discharge of the refuse matter. Each part of this -extended apparatus is modified in structure so as specially to fit it -for the performance of the office which is appropriated to it. - -564. The mouth is not merely the opening between the two lips, but -consists of an oval chamber, bounded above by the upper jaw and the -palate; below by the tongue and the lower jaw; laterally by the cheeks; -behind by the soft palate; and before by the lips. - -565. The upper and lower jaw, the palate bones, and the teeth, -constitute the hard or the bony parts of the mouth. The soft parts -consist of the lips, the cheeks, the soft palate, the tongue, and the -mucous membrane which lines the whole. - -566. The lips and cheeks are composed principally of muscles, covered -on the outside by the skin, and lined on the inside by the mucous -membrane of the mouth. In the interspaces between the muscles is -disposed a quantity of fat, which gives form to the face, facilitates -the movements of the muscles, and protects the glands, blood-vessels, -and nerves, with which all these organs are most abundantly supplied. - -567. The roof of the mouth, called the palate, consists partly of bony -and partly of membranous substance. The bony part of the palate forms -an arch in the upper jaw, the position of which in the erect posture is -horizontal: the membranous part of the palate consists of the mucous -membrane of the mouth, which affords a covering to the bony part of the -palate. - -[Illustration: Fig. CLII.—_View of the Mouth, showing particularly the -Soft Palate, Tonsils, and Tongue._ - - 1. Anterior arch of the soft palate. 2. Posterior arch. 3. Tonsils or - amygdalæ. 4. Uvula. 5. Communication between the mouth and pharynx. - 6. The tongue. 7. Anterior or nervous papillæ. 8 and 9. The upper and - lower turbinated bones dividing the nostrils into (10) chambers.] - -[Illustration: Fig. CLIII.—_A side view of the Mouth, Pharynx, Nose, -&c._ - - 1. Mouth. 2. Tongue. 3. Section of the lower jaw. 4. Submaxillary - gland. 5. Sublingual gland. 6. Hyoid bone. 7. Thyroid cartilage. 8. - Thyroid gland. 9. Trachea. 10. Interior of the pharynx. 11. Section - of the soft palate. 12. The esophagus. 13. The interior of the nose. - 14. The two spongy bones dividing it into three chambers. 15. The - posterior communication with the upper part of the pharynx.] - -[Illustration: Fig. CLIV.—_Posterior view of the Nose, Mouth, Larynx, -and Pharynx laid open._ - - 1. Posterior openings of the nose, communicating with the upper part - of the pharynx. 2. Posterior surface of the soft palate. 3. The uvula. - 4. Back part of the mouth communicating with the pharynx. 5. The - tonsils. 6. Back part or root of the tongue. 7. Posterior surface of - the epiglottis. 8. The larynx. 9. The opening of the larynx into the - pharynx. 10. Cut edges of the pharynx. 11. Esophagus, the continuation - of the pharynx. 12. The Trachea, continuation of the larynx. 13. - Muscles acting on the pharynx.] - -568. From the posterior part of the bony arch of the palate is -suspended, transversely, a moveable partition, called the soft palate -(fig. CLII. 1 and 2), which is composed of muscular fibres enclosed -in the mucous membranes of the mouth. No less than ten distinct -muscles enter into the composition of the soft palate. These muscles -are disposed in such a manner that they render the organ capable of -descending and of applying itself against the tongue (fig. CLII. 6), so -as completely to close the passage between the mouth and the pharynx -(figs. CLII. 5, and CLIV. 1), and of ascending and carrying itself -obliquely backwards towards the posterior wall of the pharynx, so as -completely to close the passage between the pharynx and the nose (fig. -CLIV. 2, 1); hence this moveable partition performs the office of a -double valve, closing the passage from the mouth to the pharynx, and -from the pharynx to the nose. - -569. From the centre of the soft palate hangs pendulous the -conical-shaped body called the uvula (fig. CLII. 4), which consists of -a small muscle enveloped in the mucous membrane of the mouth. The uvula -assists in completing the valve formed by the soft palate (fig. CLIV. -2, 3); it is also an important organ in the modulation of the voice. -When destroyed by disease, both the deglutition of the food and the -sound of the voice become imperfect. - -570. The lateral edges of the soft palate separate into two layers, -which enclose between them the bodies called the tonsils (fig. CLII. -3), two glands commonly about the size of an almond. These organs -co-operate with other glands in secreting the fluids of the mouth. - -571. The tongue (figs. CLII. 6, and CLIII. 2) is composed of six -distinct muscles enveloped in the mucous membrane of the mouth. The -fibres of these muscles are so interwoven with each other as to form -an intricate net-work; and their number, arrangement, and exquisite -organization render the organ capable of executing a surprising variety -of movements with the most perfect precision, and with a velocity -of which the mind can scarcely form a conception: some of these -movements being requisite to bring the aliment under the operation of -mastication, and others to produce articulate speech. - -572. The tongue divided into base, apex, and dorsum, is supported by a -bone called the hyoid bone (os hyoides) (figs. CXXXVI. 1, and CLIII. -6), which, unlike any other bone of the body, is placed at a distance -from the general skeleton, and completely imbedded in muscles. This -singularly posted and delicately constructed bone is not only connected -with the tongue, but with many other highly important muscles, to which -it affords a support and a lever. - -573. Each jaw is provided with sixteen teeth (fig. CLV.), arranged with -perfect uniformity, eight on each side of each jaw (fig. CLV.); those -of the one side exactly corresponding with those of the other (fig. -CLV.). The teeth, from the differences they present in their size, -form, mode of connection with the jaw, and use, are divided into four -classes, namely, on each side of each jaw, two incisors (figs. CLVI. -and CLVII. 1, 2); one cuspid (figs. CLVI. and CLVII. 3); two bicuspid -(figs. CLVI. and CLVII. 4, 5); and three molars (figs. CLVI. and CLVII. -6, 7, 8). - -[Illustration: Fig. CLV. - - A lateral view of the whole series of the teeth, in situ, showing the - relative situation of those of the upper with those of the lower jaw. - This figure and the following figures to 159, are copied from Mr. T. - Bell’s scientific and instructive work on the Anatomy, Physiology, and - Diseases of the Teeth.] - -574. The incisor, or cutting teeth, are situated in the front of the -jaw; that directly in the centre is called the central; and the next -to it the lateral incisor (fig. CLV.). Their office, as their name -imports, is to cut the food, which they do, on the principle of shears -or scissors. - -575. Standing next to the lateral incisor is the cuspid, canine, or -eye-tooth (figs. CLV., CLVI., and CLVII.). It is the longest of all the -teeth. Its office is to tear such parts of the food as are too hard to -be readily divided by the incisors. - -576. Next the cuspid are the bicuspid, two on each side (fig. CLV., -CLVII.), so named from their being provided with two distinct -prominences or points. Their office is to tear tough substances -preparatory to their trituration by the next set. - -[Illustration: Fig. CLVI. - - Front or external view of the upper teeth. 1. The central incisor. - 2. The lateral incisor. 3. The cuspid. 4. The first bicuspid. 5. The - second bicuspid. 6. The first molar. 7. The second molar. 8. The third - molar, or dens sapientiæ.] - -577. The molars, or the grinders, three on each side (fig. CLVI. -and CLVII.), provided with four or five prominences on the grinding -surface, with corresponding depressions, which are so arranged that -the elevations of those of the upper are adapted to the concavities of -those of the lower jaw, and the contrary. - -[Illustration: Fig. CLVII. - - Front view of the lower teeth. 1. The central incisor. 2. The lateral - incisor. 3. The cuspid. 4. The first bicuspid. 5. The second bicuspid. - 6. The first molar. 7. The second molar. 8. The third molar, or dens - sapientiæ.] - -578. From the incisor to the molar teeth there is a regular gradation -in size, form, and use, the cuspid holding a middle place between the -incisor and the bicuspid, and the bicuspid being in every respect -intermediate between the cuspid and the molar. Thus the incisor are -adapted only for cutting, the cuspid for tearing, the bicuspid partly -for tearing and partly for grinding, and the molar solely for grinding. -The incisor has only a single root, which is nearly round, and quite -simple (fig. CLVII. 1, 2); the cuspid has only a single root, but this -is flattened and partially grooved (fig. CLVII. 3); even the bicuspid -has only a single root, but this is commonly divided at its extremity, -and is always so much grooved as to have the appearance of two fangs -partially united, the body having two points instead of one, thus -approaching it to the form of the molar (fig. CLVII. 4, 5); and these -last have always two, sometimes three, occasionally four roots, and -their body is greatly increased in size, and has a complete grinding -surface (fig. CLVII. 6, 7, 8). - -579. In some animals whose food and habits require the utmost extension -of the office of a particular class of teeth, a corresponding -development of that class takes place. Thus in the carnivora, as is -strikingly seen in the tiger and the polar bear, the cuspid or canine -teeth are prodigiously elongated and strengthened, in order to enable -them to seize their food, and to tear it in pieces. On the other hand, -in the rodentia, or gnawing animals, as in the beaver, the incisors -are exceedingly elongated; while in the graminivora, and especially in -the ruminantia, the molar teeth are by far the most developed. In each -case the other kinds of teeth are of little comparative importance; -sometimes they are even altogether wanting. Thus the shark has only one -kind of tooth, the incisor; but of these there are several rows, and -all of them the creature has the power of erecting at will. - -580. So intimately are these organs connected with the kind of food -by which life is sustained, and the kind of food with the general -habits of the animal, that an anatomist can tell the structure of -the digestive organs, the kind of nervous system, the physical and -even the mental endowments; that is, the exact point in the scale of -organization to which the animal belongs, merely by the inspection of -the teeth. - -581. In man, the several classes of the teeth are so similarly -developed, so perfectly equalized, and so identically constructed, that -they may be considered as the true type from which all the other forms -are deviations. - -582. For the accomplishment of their office the teeth must be endowed -with prodigious strength: for the fulfilment of purposes immediately -connected with the apparatus of digestion, it is necessary that they -should be placed in the neighbourhood of exceedingly soft, delicate, -irritable, and sentient organs. That they may possess the requisite -degree of strength, they are constructed chiefly of bone, the hardest -organized substance. Bone, though not as sensible as some other parts -of the body, is nevertheless sentient. The employment of a sensitive -body in the office of breaking down the hard substances used as food -would be to change the act of eating from a pleasurable into a painful -operation. It has been shown (vol. i. p. 84) that provision is made -for supplying to the animal a never-failing source of enjoyment in the -annexation of pleasurable sensations with the act of eating, and that, -taking the whole of life into account, the sum of enjoyment secured by -this provision is incalculable. But all this enjoyment might have been -lost, might even have been changed into positive pain, nay, must have -been changed into pain, but for adjustments numerous, minute, delicate, -and, at first view, incompatible. - -583. Had a highly-organized and sensitive body been made the instrument -of cutting, tearing, and breaking down the food, every tooth, every -time it comes in contact with the food, would produce the exquisite -pain now occasionally experienced when a tooth is inflamed. Yet a -body wholly inorganic and therefore insensible, could not perform the -office of the instrument; first, because a dead body cannot be placed -in contact with living parts without producing irritation, disease, and -consequently pain; and, secondly, because such a body being incapable -of any process of nutrition, must speedily be worn away by friction, -and there could be no possibility of repairing or of replacing it. The -instrument in question, then, must possess hardness, durability, and, -to a certain extent, insensibility; yet it must be capable of forming -an intimate union with sentient and vital organs, must be capable of -becoming a constituent part of the living system. - -584. To communicate to it the requisite degree of hardness, the hard -substance forming its basis is rendered so much harder than common bone -that some physiologists have even doubted whether it be bone, whether -it really possess a true organic structure. That there is no ground for -such doubt the evidence is complete. For, - -1. The tooth, like bone in general, is composed partly of an earthy -and partly of an animal substance; the earthy part being completely -removable by maceration in an acid, and the animal portion by -incineration, the tooth under each process retaining exactly its -original form. - -2. The root of the tooth is covered externally by periosteum; its -internal cavity is lined by a vascular and nervous membrane, and both -structures are intimately connected with the substance of the tooth. If -these membranes really distribute their blood-vessels and nerves to the -substance of the tooth, which there is no reason to doubt, the analogy -is identical between the structure of the teeth and that of bone. - -3. Though the blood-vessels of the teeth are so minute that they do -not, under ordinary circumstances, admit the red particles of the -blood, and though no colouring matter hitherto employed in artificial -injections has been able, on account of its grossness, to penetrate -the dental vessels, yet disease sometimes accomplishes what art is -incapable of effecting. In jaundice the bony substance of the teeth is -occasionally tinged with a bright yellow colour; and in persons who -have perished by a violent death, in whom the circulation has been -suddenly arrested, it is of a deep red colour. Moreover, when the -dentist files a tooth, no pain is produced until the file reaches the -bony substance; but the instant it begins to act upon this part of the -tooth, the sensation becomes sufficiently acute. - -585. These facts demonstrate that the bony matter of the tooth, though -modified to fit the instrument for its office, is still a true and -proper organized substance. - -586. Each tooth is divided into body, neck, and root (fig. CLVIII. 1, -2, 3). The body is that part of the tooth which is above the gum, the -root that part which is below the gum, and the neck that part where the -body and the root unite (fig. CLVIII.). The body, the essential part, -is the tooth properly so called, the part which performs the whole work -for which the instrument is constructed, to the production and support -of which all the other parts are subservient. - -[Illustration: Fig. CLVIII. - - Views of different kinds of teeth, showing their anatomical division - into, 1. The body or crown. 2. The fang or root. 3. The neck.] - -[Illustration: Fig. CLIX.—Sections of Teeth, exhibiting their Structure. - - 1. The bony substance. 2. The enamel. 3. The internal cavity. 4. The - foramen, or hole at the extremity of the root.] - -587. When a vertical section is made in the tooth, it is found to -contain a cavity of considerable size (fig. CLIX, 3), termed the dental -cavity, which, large in the body of the tooth, gradually diminishes -through the whole length of the root (fig. CLIX. 3). The dental cavity -is lined throughout with a thin, delicate, and vascular membrane, -continued from that which lines the jaw. It contains a pulpy substance. -This pulp, highly vascular and exquisitely sensible, is composed almost -entirely of blood-vessels and nerves, and is the source whence the bony -part of the tooth derives its vitality, sensibility, and nutriment. The -blood-vessels and nerves that compose the pulp enter the dental cavity -through a minute hole at the extremity of the root (fig. CLIX. 4). The -membrane which lines the dental cavity is likewise continued over the -external surface of the root, so as to afford it a complete envelope. - -588. Provision having been thus made for the organization of the tooth, -for the support of its vitality, and for its connexion with the living -system, over all that portion of it which is above the gum, and which -constitutes the essential part of the instrument, there is poured a -dense, hard, inorganic, insensible, all but indestructible substance, -termed enamel (fig. CLIX. 2); a substance inorganic, composed of earthy -salts, principally phosphate of lime with a slight trace of animal -matter: a substance of exceeding density, of a milky-white colour, -semi-transparent, and consisting of minute fibrous crystals. The manner -in which this inorganic matter is arranged about the body of the tooth -is worthy of notice. The crystals are disposed in radii springing from -the centre of the tooth (fig. CLX. 3); so that the extremities of the -crystals form the external surface of the tooth, while the internal -extremities are in contact with the bony substance (fig. CLX. 3). By -this arrangement a two-fold advantage is obtained; the enamel is less -apt to be worn down by friction, and is less liable to accidental -fracture. - -[Illustration: Fig. CLX. - - Magnified section of a tooth, to illustrate the arrangement of the - fibrous crystals composing the enamel. 1. Cavity of the tooth. 2. Bony - substance. 3. Enamel, showing the crystals disposed in radii.] - -589. In this manner an instrument is constructed possessing the -requisite hardness, durability, and insensibility; yet organized, -alive, as truly an integrant portion of the living system as the eye or -the heart. - -590. No less care is indicated in fixing than in constructing the -instrument. It is held in its situation not by one expedient, but by -many. - -1. All along the margin of both jaws is placed a bony arch, pierced -with holes, which constitute the sockets, called alveoli, for the teeth -(fig. CLXI.). Each socket or alveolus is distinct, there being one -alveolus for each tooth (fig. CLXI.). The adaptation of the root to -the alveolus is so exact, and the adhesion so close, that each root is -fixed in its alveolus just as a nail is fixed when driven into a board. - -[Illustration: Fig. CLXI. - - Upper jaw, showing the alveoli.] - -2. The roots of the tooth, when there are more than one, deviate -from a straight line (fig. CLVI. 6, 7, 8); and this deviation from -parallelism, on an obvious mechanical principle, adds to the firmness -of the connexion. - -3. Adherent by one edge to the bony arch of the jaw, and by the other -to the neck of the tooth, is a peculiar substance, dense, firm, -membranous, called the gum, less hard than cartilage, but much harder -than skin, or common membrane; abounding with blood-vessels, yet but -little sensible; constructed for the express purpose of assisting to -fix the teeth in their situation. - -4. The dense and firm membrane covering the bony arch of the jaw is -continued into each alveolus which it lines; from the bottom of the -alveolus this membrane is reflected over the root of the tooth, which -it completely invests as far as the neck, where it terminates, and -where the enamel begins: this membrane, like a tense and strong band, -powerfully assists in fixing the tooth. - -5. Lastly, the vessels and nerves which enter at the extremity of the -root, like so many strings, assist in tying it down; hence, when in the -progress of age, all the other fastenings are removed, these strings -hold the teeth so firmly to the bottom of the socket, that their -removal always requires considerable force. - -591. But a dense substance like enamel, acting with force against so -hard a substance as bone, would produce a jar which, propagated along -the bones of the face and skull to the brain, would severely injure -that tender organ, and effectually interfere with the comfort of eating. - -592. This evil is guarded against, - -1. By the structure of the alveoli (fig. CLXII.), which are composed -not of dense and compact, but of loose and spongy bone (fig. CLXII.). -This cancellated arrangement of the osseous fibres is admirably -adapted for absorbing vibrations and preventing their propagation (90). - -2. By the membrane which lines the socket. - -3. By the membrane which covers the root of the tooth; and, - -4. By the gum. - -[Illustration: Fig. CLXII. - - View of the upper and lower teeth in the alveoli; the external - alveolar plate being cut away to show the cancellated structure of the - alveoli, and the articulation of the teeth.] - -These membranous substances, even more than the cancellated structure -of the alveoli, absorb vibrations and counteract the communication of -a shock to the bones of the face and head when the teeth act forcibly -on hard materials; so many and such nice adjustments go to secure -enjoyment, nay to prevent exquisite pain, in the simple operation of -bringing the teeth into contact in the act of eating. - -[Illustration: Fig. CLXIII.—_View of the Muscles of Mastication, which -elevate the lower jaw._ - - 1. The temporal muscle. 2. Its insertion passing beneath. 3. The - zygoma. 4. The masseter muscle, its anterior portion reflected to show - the insertion of the temporal. The action of these powerful muscles - is to pull the lower jaw upwards with great force against the upper - jaw, and at the same time to draw it a little forwards or backwards, - according to the direction of the fibres of the muscles.] - -593. The teeth in mastication are passive instruments put in motion -by the jaws. The upper jaw is fixed, the lower only is movable. The -lower jaw is capable of four different motions; depression, elevation, -a motion forwards and backwards, and partial rotation. These simple -motions are capable, by combination, of producing various compound -motions. Numerous muscles, some of them endowed with prodigious power, -are so disposed and combined as to be able, at the command of volition, -to produce any of these motions that may be required, simple or -compound. - -[Illustration: Fig. CLXIV.—_Muscles of the Jaw._ - - 1. Portion of the zygomatic process of the temporal bone. 2. Ascending - plate of the lower jaw removed to expose, 3. External pterygoid, and, - 4. Internal pterygoid muscles. The action of these muscles is to raise - the lower jaw, and to pull it obliquely towards the opposite side. - When both muscles act together, they bring the lower jaw forwards, so - as to make the fore-teeth project beyond those of the upper jaw.] - -594. By the combination, succession, alternation, and repetition of -these motions, the lower is made to produce upon the upper jaw all the -variety of pressure necessary for the mastication of the food. In this -process the muscles of the tongue perform scarcely a less important -part than the muscles of the lower jaw. Some of its muscular fibres -shorten the tongue, some give it breadth, others render it concave, -and others convex: so ample is the provision for moving this organ to -different parts of the mouth and fauces, whether to bruise the softer -parts of the aliment against the palate, to mix it with the saliva, or -to place it under the pressure of the teeth. - -595. By the combined action of the muscles of the lower jaw and tongue, -and that of the teeth, the food is bruised, cut, torn, and divided -into minute fragments. This operation is of so much importance that -the whole process of digestion is imperfect without it. It is proved -by direct experiment that the stomach acts upon the aliment with a -facility in some degree proportionate to the perfection with which it -is masticated. If an animal swallow morsels of food of different bulks, -and the stomach be examined after a given time, digestion is found to -be the most advanced in the smallest pieces, which are often completely -softened, while the larger are scarcely acted upon at all. - -596. At the same time that, by the operation of mastication, the -aliment undergoes mechanical division, it imbibes a quantity of fluid -derived from various sources. - -1. From the membrane which lines the internal surface of the mouth, and -which affords a covering to all the parts contained in it. - -2. From numerous minute glands placed in clusters about the cheeks, -gums, lips, palate, and tongue. Each of these glands is furnished -with its own little duct, which, piercing the mucous membrane, opens -into the cavity of the mouth. From these glands is derived the fluid -with which the interior of the mouth is lubricated. It consists of a -glutinous, adhesive, transparent fluid, of a light grey tint, salt -taste, and slightly alkaline nature, termed mucus. - -[Illustration: Fig. CLXV.—_View of the Parotid Gland with the Muscles -of the Face._ - - 1. Parotid gland. 2. Parotid duct. 3. Masseter muscle. 4. Buccinator. - 5. Triangularis, or depressor of the angle of the mouth. 6. Depressor - of the lower lip. 7. Orbicularis, or circular muscle of the mouth. 8. - Great zygomatic, or the distorter of the mouth, as in laughing. 9. - Elevator of the angle of the mouth. 10. Elevator of the upper lip, - and wing of the nose. 11. Compressor of the cartilage of the nose. - 12. Orbicularis, or circular muscle of the eyelids. 13. Occipito - frontalis; elevator of the eyelids; motor of the scalp, &c., an - important muscle of expression. 14. Tendinous portion of the occipito - frontalis. 15. Elevator of the ear.] - -3. From six large glands placed symmetrically, three on each side, -termed the salivary glands, namely, the parotid (fig. CLXV. 1), -situated before the ear; the submaxillary (fig. CLIII. 4), situated -beneath the lower jaw; and the sublingual (fig. CLIII. 5), situated -immediately under the tongue. Each of these glands is provided with a -duct (figs. CLXV. 2, and cliii. 4, 5), by which it pours the fluid it -elaborates, called saliva, into the mouth. - -597. The other fluids of the mouth are always mixed with the saliva, -and are all commonly included under that name. The secretion of these -fluids is unceasing, and they pass into the stomach by successive acts -of deglutition at nearly regular intervals; so that the stomach, after -it has been some time without food, contains a considerable quantity -of these fluids. But they are chiefly needed during the operation of -mastication, and two provisions are made for securing their flow in the -greatest abundance at that time. - -598. First, the situation of the glands is such that they are all -exposed to the action of the muscles of mastication (figs. CLXIII. and -CLXIV.), by which action the glands are excited, a large quantity of -blood is determined to them, and the quantity of fluid they secrete -is proportionate to the quantity of blood they receive. Secondly, the -glands are placed under the influence of the mind, so that the very -thought, and still more the taste, of grateful food, acting upon them -as an additional stimulus, causes an additional secretion. The quantity -of fluid formed from these different sources, and mixed with the food -during the mastication of an ordinary meal, is estimated at half a -pint. It must commonly be more than this, because, in a case described -by Dr. Gairdner, of Edinburgh, in which the esophagus had been cut -through, it was observed that from six to eight ounces of saliva were -discharged during a meal, which consisted merely of broth injected -through the divided esophagus into the stomach. - -599. Saliva is a frothy, watery fluid, in its healthy state nearly -insipid, and of a slightly alkaline nature. It is composed of water, -a peculiar animal substance called salivary matter, mucus, osmazome, -a little albumen, and several salts. It produces important changes -on the food. By the water, and the salts contained in it, it softens -and dissolves the food; and thus, while it renders it easier to -be swallowed, it prepares it for the subsequent changes it is to -undergo. To this latter object, the assimilation of the food, it -seems to communicate the first tendency by the azotized substances, -the salivary, and the albuminous matter which it adds to it. From -this, the commencement of the assimilative process to its completion, -animalized substances are successively added to the food which have the -property of converting the food more and more into the nature of animal -substance. - -600. Comminuted by the teeth, and softened by the saliva, the food is -reduced to a pulp. In this pulp there is a complete admixture of all -the alimentary substances with the assimilative matter secreted from -the blood, into the nature of which it is to be ultimately changed. The -mass is at the same time brought to the temperature of the blood. - -601. As long as the operations of mastication and insalivation go on, -the mouth forms a closed cavity from which the food cannot escape; for -the lips enclose it before, the cheeks at the sides, the tongue below, -and the soft palate behind, the inferior edge of which being applied -in close and firm contact with the base of the tongue, prevents all -communication between the mouth and the pharynx. - -602. When, by mastication, the food is sufficiently divided, and by -insalivation softened and animalized to fit it for the future changes -it is to undergo, it is collected by the tongue, and carried by that -organ to the back part of the mouth. The soft palate (fig. CLII. 1), -obedient to the stimulus of the duly prepared food, rises the instant -it is touched by it, and affords it a free passage to the pharynx -(figs. CLIII. 10, and CLIV. 10). - -603. The pharynx (fig. CLIII. 10), a muscular bag, immediately -continuous with the mouth (fig. CLIII. 1), is a vestibule into which -open several highly important organs. Before is the entrance to the -windpipe, termed the glottis (fig. CLIV. 9), leading directly to the -larynx (fig. CLIV. 8); at the sides are the mouths of two ducts, termed -the Eustachian tubes, which lead to the internal part of the organ of -hearing; above are two entrances to the nose (fig. CLIV. 1); and below -is the passage to the stomach (fig. CLIII. 12). - -604. Were the food to enter the Eustachian tubes or the nose, it would -occasion great inconvenience; were it to enter the glottis, it would -cause death. It is prevented from entering the Eustachian tubes and the -nose by the soft palate (fig. CLII. 1 and 2), which by the very act of -rising to afford an opening from the mouth to the pharynx, is carried -over the other apertures so as completely to close them. By the varied -direction of the muscular fibres which enter into the composition of -this organ, it is enabled to execute the different and even opposite -motions required in the performance of its important office. - -605. The food is prevented from entering the glottis partly by a -cartilaginous valve (fig. CLIV. 7), termed the epiglottis, placed -immediately above the glottis, and attached to the root of the tongue -(fig. CLIV. 6). In delivering the food to the pharynx the tongue passes -backwards (fig. CLIV. 6). In passing backwards it pushes in the same -direction the epiglottis which is attached to it, and so necessarily -carries it over the glottis, completely closing the aperture (fig. -CLIV. 9). At the same time the opening is still more securely closed -by the glottis itself, in consequence of the powerful and simultaneous -contraction of the muscles that act upon it in the production of the -voice. It is proved, by direct experiment, that the spontaneous closure -of the glottis is a more powerful agent in excluding the food from the -larynx even than the depression of the epiglottis; but both organs -concur in producing the same result; and a double security is provided -against an event which would be fatal. - -606. It is deeply interesting to observe the part performed in these -operations by sensation and volition, and the boundary at which their -influence terminates and consciousness itself is lost. Mastication, a -voluntary operation, carried on by voluntary muscles, at the command -of the will, is attended with consciousness, always in the state of -health of a pleasurable nature. To communicate this consciousness, the -tongue, the palate, the lips, the cheeks, the soft palate, and even -the pharynx, are supplied with a prodigious number of sentient nerves. -The tongue especially, one of the most active agents in the operation, -is supplied with no less than six nerves derived from three different -sources. These nerves, spread out upon this organ, give to its upper -surface a complete covering, and some of them terminate in sentient -extremities visible to the naked eye. These sentient extremities, -with which every point of the upper surface, but more especially the -apex, is studded, constitute the bodies termed papillæ, the immediate -and special seat of the sense of taste. This sense is also diffused, -though in a less exquisite degree, over the whole internal surface -of the mouth. Close to the sense of taste is placed the seat of the -kindred sense of smell. The business of both these senses is with the -qualities of the food. Mastication at once brings out the qualities -of the food and puts the food in contact with the organs that are to -take cognizance of it. Mastication, a rough operation, capable of -being accomplished only by powerful instruments which act with force, -is carried on in the very same spot with sensation, an exquisitely -delicate operation, having its seat in soft and tender structures, -with which the appropriate objects are brought into contact only with -the gentlest impulse. The agents of the coarse and the delicate, the -forcible and the gentle operations are in close contact, yet they -work together not only without obstruction, but with the most perfect -subserviency and co-operation. - -607. The movements of mastication are produced, and, until they have -accomplished the objects of the operation, are repeated by successive -acts of volition. To induce these acts, grateful sensations are excited -by the contact of the food with the sentient nerves so liberally -distributed over almost the whole of the apparatus. To the provision -thus made for the production of pleasurable sensation, is superadded -the necessity of direct and constant attention to the pleasure -included in the gratification of the taste. It is justly observed by -Dr. A. Combe, that without some degree of attention to the process of -eating, and some distinct perception of its gratefulness, the food -cannot be duly digested. When the mind is so absorbed as to be wholly -unconscious of it, or even indifferent to it, the food is swallowed -without mastication; then it lies in the stomach for hours together -without being acted upon by the gastric juice, and if this be done -often, the stomach becomes so much disordered as to lose its power of -digestion, and death is the inevitable result: so that not only is -pleasurable sensation annexed to the reception of food, but the direct -and continuous consciousness of that pleasurable sensation during the -act of eating is made one of the conditions of the due performance of -the digestive function. - -608. With the operation of mastication and one part of the process of -deglutition, immediately to be noticed, the agency of volition and -sensation cease. Beyond this the function of digestion is wholly an -organic process. In addition to the reasons assigned (vol. i. p. 55) -why all the organic processes are placed alike beyond the cognizance of -sense and the control of the will, there is this special reason why, in -the function of digestion, they cease at the exact boundary assigned -them. - -609. Every time the act of deglutition is performed the openings to the -windpipe and to the nose are closed, so that during this operation all -access of air to the lungs is stopped, consequently it is necessary -that the passage of the food through the pharynx should be rapid. -Mastication, a voluntary process, may be performed slowly or rapidly, -perfectly or imperfectly, without serious mischief; but life depends on -the passage of the food through the pharynx with extreme rapidity and -with the nicest precision. It is therefore taken out of the province -of volition and entrusted to organs which belong to the organic life, -organs which carry on their operations with the steadiness, constancy, -and exactness of bodies whose motions are determined by a physical law. - -610. No sooner does the duly-prepared food touch the soft palate than -the whole apparatus of deglutition is instantly in motion. This movable -partition suddenly rises to afford to the food a free passage to the -pharynx. The pharynx itself, at the same instant, rises to receive the -morsel thrust towards it by the pressure of the tongue; and one muscle, -the stylo-pharyngeus, which concurs in producing this movement, seems -specially intended, in addition, to expand the pharynx. Three muscles -throw their fibres around the pharynx, termed its upper, middle, and -lower constrictors, which, the moment the morsel reaches the pharynx, -contract upon it, and embrace it firmly. At the same instant the -larynx, closing its aperture, springs forward towards the base of the -tongue, under which it is in a manner concealed, the additional shield -of the epiglottis being simultaneously thrown over the glottis. By this -movement of the larynx, upwards and forwards, the course of the morsel -across the dangerous passage is shortened. All these motions take -place with such rapidity that Boerhaave said the action is convulsive. -And now the food, firmly pressed by the pharynx, cannot return to the -mouth, for the root of the tongue is there stopping up the passage; it -cannot enter the Eustachian tubes or the nose, for the soft palate is -there closing the apertures; it cannot enter the larynx, for a double -guard is placed upon the glottis securing its firm closure. The food -can advance in one direction only, the direction required, that which -leads to the esophagus. Well, therefore, on the contemplation of these -complex structures and the consent and harmony with which they act, -might Paley say, “In no apparatus put together by art do I know such -multifarious uses so aptly contrived as in the natural organization of -the human mouth and its appendages. In this small cavity we have teeth -of different shape; first, for cutting; secondly, for grinding; muscles -most artificially disposed for carrying on the compound motions of the -lower jaw by which the mill is worked; fountains of saliva springing up -in different parts of the cavity for the moistening of the food while -the mastication is going on; glands to feed the fountains; a muscular -contrivance in the back part of the cavity for the guiding of the -prepared aliment into its passage towards the stomach, and for carrying -it along that passage. In the mean time, and within the same cavity, -is going on other business wholly different, that of respiration and -of speech. In addition, therefore, to all that has been mentioned, -we have a passage opened from this same cavity of the mouth into the -lungs for the admission of air, for the admission of air exclusively -of every other substance; we have muscles, some in the larynx, and, -without number, in the tongue, for the purpose of modulating that air -in its passage, with a variety, a compass, and a precision of which no -other musical instrument is capable; and, lastly, we have a specific -contrivance for dividing the pneumatic part from the mechanical, and -for preventing one set of functions from interfering with the other. -The mouth, with all these intentions to serve, is a single cavity; is -one machine, with its parts neither crowded nor confined, and each -unembarrassed by the rest.” It should be added, the mouth is also the -immediate seat of one of the senses, and is in intimate communication -with a second sense; both these senses are always excited while the -principal business performed by the machine is carried on, and are -necessarily excited by the very working of the machine, and the -sensations induced in the natural and sound state of the apparatus are -invariably pleasurable. - -611. The food is delivered by the pharynx to the esophagus (fig. -CLIII. 12), a tube composed partly of membrane and partly of muscle. -Its muscular fibres consist of a double layer, an external and an -internal layer; the external has a longitudinal direction; the internal -describes portions of a circle around the tube. By the contraction -of the longitudinal fibres the length, and by the contraction of the -circular fibres, the diameter of the tube is diminished. Cellular -membrane envelops these layers of fibres externally, and mucous -membrane covers them internally. When the tube is contracted, the -mucous membrane is disposed in folds, which disappear when it is -dilated, and these folds allow of the expansion of the tube without -injury to the delicate tissue that lines it. The food passes slowly -along the esophagus urged towards the stomach, not by its own gravity, -but by a force exerted upon it by the tube itself, chiefly by the -contraction of its circular fibres. Delivered at length to the -stomach, the food is incapable of returning into the esophagus in -consequence of the oblique direction in which the esophagus enters the -stomach, the obliquity of its entrance serving the office of a valve. - -[Illustration: Fig. CLXVI.—_View of the Stomach with its Muscular Coats -displayed._ - - 1. The esophagus terminating in the stomach. 2. The cardiac orifice. - 3. The pylorus. 4. The commencement of the duodenum. 5. The large - curvature of the stomach. 6. The small curvature. 7. The large - extremity. 8. The small extremity. 9. The longitudinal muscular - fibres. 10. The circular muscular fibres.] - -612. The stomach is a bag of an irregular oval shape (fig CLXVI.), -capable, in the adult, of containing about three pints. It is placed -transversely across the upper part of the abdomen (fig. LX. 7). It -occupies the whole epigastric (fig. CV. 3), and the greater part of -the left hypochondriac regions (fig. CVII. 3). Above, it is in contact -with the diaphragm, the arch of which extends over it (fig. LX. 7, b); -below with the intestines (fig. LX. 8, 9), on the right side with the -liver (fig. LX. 6), and on the left side with the spleen (fig. CLXVIII. -5). - -[Illustration: Fig. CLXVII. _Internal View of the Stomach and Duodenum._ - - 1. Mucous membrane, forming the rugæ. 2. Pyloric orifice opening into - the duodenum. 3. Duodenum. 4. Interior of the duodenum, showing the - valvulæ conniventes. 5. Termination of, 6. The biliary or choledoch - duct. 7. Pancreatic duct, terminating at the same point as the - choledoch duct. 8. Gall-bladder removed from the liver. 9. Hepatic - duct proceeding from the liver. 10. Cystic duct proceeding from the - gall-bladder, forming by its union with the hepatic, a common trunk, - the choledoch.] - -613. Into the left extremity, which is much larger and considerably -higher than the right (fig. CLXVI. 7), the esophagus opens by an -aperture called the cardiac orifice (fig. CLXVI. 2). At the right -extremity, a second aperture called the pyloric orifice (fig. CLXVII. -2), leads into the first intestine. - -614. Between the cardiac and the pyloric orifices are two curvatures, -one above, called the smaller (fig. CLXVI. 6), the other below, termed -the larger curvature (fig. CLXVI. 5). - -615. Like the esophagus, the stomach is composed of two layers of -muscular fibres, the external longitudinal (fig. CLXVI. 9), the -internal circular (fig. CLXVI. 10). By the contraction of the first the -extent of the stomach, from extremity to extremity, is diminished, or -the organ is shortened; by the contraction of the second the extent of -the stomach, from curvature to curvature, is diminished, or the organ -is narrowed. During digestion, by the contraction of these muscular -fibres, the capacity of the stomach is changed alternately in both -directions, whence a gentle motion is communicated to the aliment, -which is thus brought in succession under the influence of the agent -that acts upon it. - -616. A thin but strong membrane, derived from the peritoneum, the -membrane that lines the general cavity of the abdomen, forms the -external tunic of the stomach; hence its outer covering is called the -peritoneal coat. - -617. The inner or mucous coat (fig. CLXVII. 1), a direct continuation -of the lining membrane of the esophagus, is sometimes called also -villous, on account of the minute bodies termed villi, with which every -point of its internal surface is studded. It is these villi which give -to this surface its pilous or velvety appearance, - -[Illustration: Fig. CLXVIII.—_View of the Vascular connexion between -the Stomach, Liver, Spleen, and Pancreas._ - - 1. Stomach raised to exhibit its posterior surface. 2. Pylorus. 3. - Duodenum. 4. Pancreas. 5. Spleen. 6. Undersurface of the liver. 7. - Gall-bladder, in connexion with the liver. 8. Large vessels proceeding - from. 9. A common trunk to supply the liver, gall-bladder, stomach, - duodenum, pancreas, and spleen.] - -618. The mucous coat is far more extensive than the other two, in -consequence of its being plaited into a number of folds (fig. CLXVII. -1), termed rugæ, which are so disposed as to present the appearance -of a net-work. The object of the rugæ is to enlarge the space for the -expansion of blood-vessels and nerves, and to admit of the occasional -distension of the organ without injury to the delicate tissues of which -it is composed. - -619. Immediately beneath the mucous coat are the mucous follicles -which secrete the mucous fluid by which the inner surface of the organ -is defended. These glandular bodies are extremely numerous, and vary -considerably in diameter. The largest are towards the great extremity, -the smaller towards the pylorus. - -620. Altogether different from the mucous secretion is another fluid, -which also flows from the mucous surface, termed the gastric or the -digestive juice, from its being the principal agent in the digestive -process. By some anatomists the gastric juice is supposed to be -secreted by minute glands placed between the mucous and the muscular -coats, provided with ducts which pierce the mucous coat, and which bear -their fluid into the stomach precisely as the salivary glands carry the -saliva into the mouth. It is certain that this is the case with some -animals, as in certain birds, the ostrich for example, in which glands -of considerable magnitude, with ducts large enough to be visible, are -seen to pour the digestive fluid into the stomach. But as no such -glands have been discovered in the human stomach, it is generally -conceived that in man the gastric juice is secreted by minute arteries -expanded upon the villi. - -621. All around the pyloric orifice (fig. CLXVII. 2) is placed a -thick, strong, and circular muscle (fig. CLXVII. 2), termed, from its -office, pylorus. It is about four times the thickness of the muscular -coat of the stomach, and presents the appearance of a prominent and -even projecting band (fig. CLXVII. 2). From the frequent action of its -fibres, the pylorus often looks as if a piece of packthread had been -tied around it (fig. CLXVI. 3). Its office is, by the contraction of -its fibres, to guard and close the opening from the stomach until the -aliment has been duly acted upon by the digestive fluid. - -[Illustration: Fig. CLXIX. - - View of the stomach, showing the number and magnitude of its - blood-vessels, and the mode of their distribution.] - -622. The quantity of blood sent to the stomach is greater than is spent -upon any other organ except the brain. The vessels of the stomach -(fig. CLXIX.) form two distinct layers, of which the external is -distributed to the peritoneal and muscular coats, while the internal, -after ramifying on the fine cellular tissue which unites the muscular -and mucous tunics, penetrates the mucous coat, and is spent upon the -villi, where it forms an exquisitely-delicate net-work. There is, -moreover, an intimate vascular connexion between the spleen, pancreas -and liver, and the stomach (fig. CLXVIII. 8, 9). The arteries which -supply all these organs spring from a common trunk, and there is the -freest communication between them by anastomosing branches. - -[Illustration: Fig. CLXX.—_View of the Organic Nerves of the Stomach._ - - 1. Under surface of the liver turned up, to bring into view the - anterior surface of the stomach. 2. Gall bladder. 3. Organic nerves - enveloping the trunks of the blood-vessels. 4. Pyloric extremity of - the stomach and commencement of the duodenum. 5. Contracted portion - of the pylorus. 6. Situation of the hour-glass contraction of the - stomach, here imperfectly represented. 7. Omentum.] - -623. Equally abundant is its supply of nerves, some of which are -derived from the organic or non-sentient system, and others from -the animal or sentient system. The organic nerves are spread out in -countless numbers upon the great trunks of the arteries, so as to give -them a complete envelope (fig. CLXX. 3); these nerves, never quitting -the arteries, accompany them in all their ramifications, and the fibril -of the nerve is ultimately lost upon the capillary termination of the -artery. It is by these organic nerves that the stomach is enabled to -perform its organic functions, which, for the reason assigned (vol. i. -p. 82), is placed beyond volition, and is without consciousness. By the -nerves derived from the sentient system which mingle with the organic -(fig. XVI.), the function of nutrition is brought into relation with -the percipient mind, and is made part of our sentient nature. By the -commixture of these two sets of nerves, derived from these two portions -of the nervous system, though we have no _direct_ consciousness of the -digestive process—consciousness ceasing precisely at the point where -the agency of volition stops (vol. i. p. 82, et seq.), yet pleasurable -sensation results from the due performance of the function. Hence -the feeling of buoyancy, exhilaration, and vigour, the pleasurable -consciousness to which we give the name of health, when the action of -the stomach is sound: hence the depression, listlessness, and debility, -the painful consciousness which we call disease, when the action of the -stomach is unsound: hence, too, the influence of the mental state over -the organic process; the rapidity and perfection with which the stomach -works when the mind is happy—when the repast is but the occasion and -accompaniment of the feast of reason and the flow of soul; the slowness -and imperfection with which the stomach works when the mind is harassed -with care struggling against adverse events; or is in sorrow and -without hope; when the friend that sat by our side, and with whom we -were wont to take sweet counsel, is gone, and therefore gone that which -made it life to live. - -624. Renovation is the primary and essential office of the stomach, -and its organic nerves enable it to supply the ever-recurring wants of -the system. Gratification of appetite is a secondary and subordinate -office of the stomach, and its sentient nerves enable it to produce -the state of pleasurable consciousness when its organic function is -duly performed. By the double office thus assigned it, the stomach is -rendered what Mr. Hunter named it, the centre of sympathies. - -625. From the whole length of the great arch of the stomach, and -partly also from the commencement of the duodenum (fig. CLXX.), the -peritoneal coat of the stomach is produced, forming a thin, delicate -membranous bag, called the omentum, or cawl (fig. CLXX. 7). The omentum -extends from the great arch of the stomach to below the umbilicus, -and completely covers a large portion of the anterior surface of the -abdominal viscera (fig. CLXX. 7). Between the two fine membranous -layers of which it is composed is contained a quantity of fat, of which -substance it serves as a reservoir, and by the transudation of which it -appears to lubricate the intestines, and to assist in preventing their -accretion. - -626. The food, on reaching the stomach, does not occupy indifferently -any portion of it, but is arranged in a peculiar manner always in one -and the same part. If the stomach be observed in a living animal, or -be inspected soon after death, it is seen that about a third of its -length towards the pylorus is divided from the rest by the contraction -of the circular fibre called the hour-glass contraction (fig. CLXX. -6). The stomach is thus divided into a cardiac and a pyloric portion -(fig. CLXX. 6). The food, when first received by the stomach, is always -deposited in the cardiac portion, and is there arranged in a definite -manner. The food first taken is placed outermost, that is, nearest the -surface of the stomach; the portion next taken is placed interior to -the first, and so on in succession, until the food last taken occupies -the centre of the mass. When new food is received before the old is -completely digested, the two kinds are kept distinct, the new being -always found in the centre of the old. - -627. Soon after the food has been thus arranged, a remarkable change -takes place in the mucous membrane of the stomach. The blood-vessels -become loaded with blood; its villi enlarge, and its cryptæ, the minute -cells between the rugæ, overflow with fluid. This fluid is the gastric -juice, which is secreted by the arterial capillaries now turgid with -blood. The abundance of the secretion, which progressively increases as -the digestion advances, is in proportion to the indigestibility of the -food, and the quietude of the body after the repast. - -628. In the food itself no change is manifest for some time; but at -length that portion of it which is in immediate contact with the -surface of the stomach begins to be slightly softened. This softening -slowly but progressively increases until the texture of the food, -whatever it may have been, is gradually lost; and ultimately the most -solid portions of it are completely dissolved. - -629. When a portion of food thus acted on is examined, it presents the -appearance of having been corroded by a chemical agent. The white of a -hard-boiled egg looks exactly as if it had been plunged in vinegar or -in a solution of potass. The softened layer, as soon as the softening -is sufficiently advanced, is, by the action of the muscular coat of -the stomach, detached, carried towards the pylorus, and ultimately -transmitted to the duodenum; then another portion of the harder and -undigested food is brought into immediate contact with the stomach, -becomes softened in its turn, and is in like manner detached; and this -process goes on until the whole is dissolved. - -630. The solvent power exerted by the gastric juice is most apparent -when the stomach of an animal is examined three or four hours after -food has been freely taken. At this period the portion of the food -first in contact with the stomach is wholly dissolved and detached; the -portion subsequently brought into contact with the stomach is in the -process of solution, while the central part remains very little changed. - -631. The dissolved and detached portion of the food, from every -part of the stomach flows slowly but steadily beyond the hour-glass -contraction, or towards the pyloric extremity (626), in which not a -particle of recent or undissolved food is ever allowed to remain. The -fluid, which thus accumulates in this portion of the stomach, is a -new product, in which the sensible properties of the food, whatever -may have been the variety of substances taken at the meal, are lost. -This new product, which is termed chyme, is an homogeneous fluid, -pultaceous, greyish, insipid, of a faint sweetish taste, and slightly -acid. - -632. As soon as the chyme, by its gradual accumulation in the pyloric -extremity amounts to about two or three ounces, the following phenomena -take place. - -633. First, the intestine called duodenum, the organ immediately -continuous with the stomach, contracts. The contraction of the duodenum -is propagated to the pyloric end of the stomach. By the contraction -of this portion of the stomach, the chyme is carried backwards from -the pyloric into the cardiac extremity, where it does not remain, -but quickly flows back again into the pyloric extremity, which is -now expanded to receive it. Soon the pyloric extremity begins again -to contract; but now the contraction, the reverse of the former, -is in the direction of the duodenum; in consequence of which, the -chyme is propelled towards the pylorus. The pylorus, obedient to the -demand of the chyme, relaxes, opens, and affords to the fluid a free -passage into the duodenum. As soon as the whole of the duly prepared -chyme has passed out of the stomach, the pylorus closes, and remains -closed, until two or three ounces more are accumulated, when the same -succession of motions are renewed with the same result; and again cease -to be again renewed, as long as the process of chymification goes on. - -634. When the stomach contains a large quantity of food, these -motions are limited to the parts of the organ nearest the pylorus; as -it becomes empty, they extend further along the stomach, until the -great extremity itself is involved in them. These motions are always -strongest towards the end of chymification. - -635. The stomach during chymification is a closed chamber; its cardiac -orifice is shut by the valved entrance of the esophagus, and its -pyloric orifice by the contraction of the pylorus. - -636. The rapidity with which the process of chymification is carried -on is different according to the digestibility of the food, the bulk -of the morsels swallowed, the quantity received by the stomach, the -constitution of the individual, the state of the health, and above -all, the class of the animal, for it is widely different in different -classes. In the human stomach in about five hours after an ordinary -meal the whole of the food is probably converted into chyme. - -637. The great agent in performing the process of chymification is the -gastric juice. The evidence of this is complete; for, - -1. As soon as the food enters the stomach a large quantity of blood is -determined to the arteries, which secrete the gastric juice (627); and -this fluid continues to be poured into the stomach in great abundance -during the whole time the process goes on. - -2. The solvent power of this fluid is demonstrated by the fact that it -sometimes dissolves the stomach itself, when death takes place suddenly -during the act of digestion in a sound and vigorous state of the -digestive organs. - -3. On introducing into the stomach alimentary substances inclosed in -metallic balls perforated with holes, or in pieces of porous cloth, -it is found, on removing these bodies from the stomach, after a -certain time, that the alimentary substances contained in them are as -completely digested as if they had been in actual contact with the -surface of the stomach; the metallic ball and the cloth remaining -wholly unchanged. This experiment, which has been often performed with -the same uniform result, was the first that led to the discovery of the -true nature of the digestive process. - -4. Though it be impossible to imitate out of the stomach all the -circumstances under which the food is placed within it, yet, on -procuring gastric juice from the stomachs of various animals, and -mixing it with different alimentary substances, it is found not only -to dissolve them, but to convert them into a pultaceous mass, closely -resembling chyme. Gastric juice thus procured was put into a glass -tube with boiled beef, which had been masticated; the tube was then -hermetically sealed, and exposed near the fire to a uniform heat: by -the side of this tube was placed another, containing the same quantity -of flesh immersed in water. In twelve hours, the flesh in the tube -containing the gastric juice began to lose its fibrous structure; in -thirty-five hours it had nearly lost its consistence, being reduced to -a soft homogeneous pultaceous mass. It experienced no further change -during the two following days. On the other hand, the flesh that had -been immersed in water was putrid in sixteen hours. - -638. Since alimentary substances under the action of the stomach -present precisely the appearance exhibited by bodies exposed to the -influence of chemical agents, it appears that the gastric juice not -only dissolves the food, but dissolves it by a chemical agency. Its -action bears no proportion to the mechanical texture of bodies, -nor to any of their physical properties. It acts upon the densest -membrane, dissolves even bone itself; and yet produces no effect on -other substances of the most tender and delicate texture. On the skin -of fruit, on the finest fibre of flax and cotton, it is incapable of -making the slightest impression. In this selection of substances it -perfectly resembles a chemical agent acting by chemical affinity. On -certain substances its action is unquestionably of a chemical nature. -It occasions the coagulation of albuminous fluids; it prevents the -accession of putrefaction; it stops the process after it has commenced. -From the whole, it follows that the food in the stomach is converted -into chyme by the agency of a fluid secreted by the inner surface of -the stomach, and that this change is effected by a proper chemical -action. - -639. It had been long ascertained that the gastric juice contains an -uncombined acid, and that if carbonate of lime be placed in a tube and -introduced into the stomach, the carbonate is dissolved just as if -it were put into weak vinegar. Several years ago, it was discovered -by Dr. Prout that this free acid is muriatic acid. Some time after -the publication of Dr. Prout’s experiments, Chevreul and Leuret and -Lassaigne in France obtained different results; but Tiedemann and -Gmelin, professors in the university of Heidelberg, in an extended -series of experiments, arrived at precisely the same conclusion as the -English physiologist, and apparently without any previous knowledge of -the researches of the latter. Tiedemann and Gmelin state, as the result -of their experiments, that the clear ropy fluid, or the gastric juice -obtained from the stomach some time after it had been without food, is -nearly or entirely destitute of acidity; that the presence of food, -or indeed of any stimulus to the mucous membrane, causes the gastric -juice to become distinctly acid; that this acidity increases according -to the indigestibility of the food; that the quantity of acid poured -out is very copious; that it consists partly of muriatic and partly -of acetic acid; and that both these acids are efficient agents in the -process of digestion. Dr. Prout, who had also recognised the presence -of acetic acid, is of opinion that its formation is an accidental -occurrence not necessary to digestion nor conducive to it; but is -either derived from the aliment, or is the result of irritation or -disease. He contends that the muriatic acid is the efficient digestive -agent. - -640. The still more recent experiments of Braconnot appear to have -set this matter at rest, and to have proved, beyond all controversy, -that the stomach, when stimulated by the presence of food or other -foreign agents, possesses the power of secreting free muriatic acid -in great quantity; and that it is by this acid that the solution of -the food is effected. It is even found that muriatic acid is capable -of digesting alimentary substances out of the body. It had been long -known, that if meat and gastric juice be inclosed in a tube and kept -at the temperature of the human body, a product is obtained closely -resembling chyme (637.4). M. Blondelot, a physician at Nancy, has -recently shown that the same result may be obtained by the digestion -of the muscular fibre, in dilute muriatic acid. In both cases the -muscular fibre retains its form and its original fibrous texture; but -on the slightest motion it divides into an insoluble mass, perfectly -homogeneous and similar to the chyme of the stomach;[5] a very close -approximation to the actual digestive process, more especially when it -is considered that it is not possible to imitate out of the stomach -several circumstances materially influencing chemical action under -which the food is placed within the stomach. - - [5] Dr. R. Thomson, British Annals of Medicine, No. 13. - -641. Muriatic acid, the chemical agent by which the stomach dissolves -the food, is probably obtained from the muriate of soda (common salt) -contained in the blood. The soda, the basis of the salt, would appear -to be retained in the blood, to preserve the alkaline condition -essential to the maintenance of the sound constitution of the blood, -while the muriatic acid, disengaged from the soda in the process of -secretion, is poured into the stomach to act upon the food. - -642. A remarkable confirmation of the correctness of the general -conclusions to which observation and experiment had thus enabled -physiologists to arrive, is afforded by the case of a young soldier -in the American army, of the name of Alexis St. Martin, who received -a wound on the left side by the accidental discharge of a musket. The -charge, which consisted of duck shot, and which was received at the -distance of one yard from the muzzle of the gun, entered the side -posteriorly in an oblique direction, forward and inward; blew off -the integument and muscles to the size of a man’s hand; fractured -and carried away the anterior half of the sixth rib; fractured the -fifth rib; lacerated the lower portion of the left lobe of the lungs; -lacerated the diaphragm, and perforated the stomach. - -643. Violent fever and extensive sloughing of the parts injured ensued, -and the life of the young man was often in jeopardy, but he ultimately -recovered. At the distance of about a year from the date of the -accident, the injured parts had all become sound, with the exception -of the perforation into the stomach, which never closed, but left an -aperture permanently open, two inches and a half in circumference. -This aperture was situated about three inches to the left of the -cardia, near the left superior termination of the great curvature. -For some time the food could be retained only by constantly wearing a -compress and bandage; but at length a small fold of the mucous coat -of the stomach appeared, which increased until it completely filled -the aperture and acted as a valve, so as effectually to prevent any -efflux from within, while it admitted of being easily pushed back by -the finger from without: when the stomach was nearly empty, it was easy -to examine its cavity to the depth of five or six inches by artificial -distension; but, when entirely empty, the stomach was always contracted -on itself, and the valve generally forced through the orifice, -together with a portion of the mucous membrane equal in bulk to a hen’s -egg. - -644. It chanced that the admirable opportunity thus afforded of -bringing the process of digestion, as far as it is carried on in the -stomach, under the cognizance of sense, occurred to an observant and -philosophical mind, and it was not lost.[6] The following are some of -the curious and instructive phenomena observed. - - [6] Experiments and Observations on the Gastric Juice, and the - Physiology of Digestion. By W. Beaumont, M.D., Surgeon in the U. S. - Army. Boston. 1834. - -645. The inner coat of the stomach, in its natural and healthy state, -is of a light or pale pink colour, varying in its hues according to its -full, or empty state. It is of a soft or velvet-like appearance (617), -and is constantly covered with a very thin transparent, viscid mucus, -lining the whole interior of the organ (619). - -646. Immediately beneath the mucous coat appear small spheroidal, or -oval-shaped glandular bodies, from which the mucous fluid appears to be -secreted (619). - -647. By applying aliment or other irritants to the internal coat of -the stomach, and observing the effect through a magnifying glass, -innumerable minute lucid points, and very fine nervous or vascular -papillæ are seen arising from the villous membrane, and protruding -through the mucous coat, from which distils a pure, limpid, -colourless, slightly viscid fluid (620). This fluid, thus excited, is -invariably distinctly acid (639, _et seq._). The _mucus_ of the stomach -is less fluid, more viscid or albuminous, semi-opaque, sometimes a -little saltish, and does not possess the slightest character of acidity -(619). On applying the tongue to the mucous coat of the stomach in its -empty, un-irritated state, no acid taste can be perceived. When food -or other irritants have been applied to the villous membrane and the -gastric papillæ excited, the acid taste is immediately perceptible. -The invariable effect of applying aliment to the internal, but exposed -part of the gastric membrane, is the exudation of the solvent fluid -from the papillæ. Though the aperture of these vessels cannot be seen -even with the assistance of the best microscopes, yet the points from -which the fluid issues are clearly indicated by the gradual appearance -of innumerable very fine lucid specks rising through the transparent -mucous coat, and seeming to burst and discharge themselves upon the -very points of the papillæ, diffusing a limpid thin fluid over the -whole interior gastric surface. - -648. The fluid so discharged is absorbed by the aliment in contact; or -collects in small drops, and trickles down the sides of the stomach to -the more depending parts, and there mingles with the food, or whatever -else may be contained in the gastric cavity. This fluid, the efficient -cause of digestion, the true gastric juice is secreted only when it -is needed; it is not accumulated in the intervals of digestion, to -be ready for the next meal; it is seldom if ever discharged from its -proper secreting vessels, except when excited by the natural stimulus -of aliment, the mechanical irritation of tubes, or other excitants. -When aliment is received, the juice is given out in exact proportion -to its requirements for solution, except when more food has been taken -than is necessary for the wants of the system. - -649. On collecting this fluid, which it was easy to obtain, it was -found to be transparent, inodorous, saltish, and acidulous to the -taste; it consisted of water, containing free muriatic and acetic -acids, phosphates and muriates, with bases of potass, soda, magnesia, -and lime, together with an animal matter soluble in cold, but insoluble -in hot water. - -650. When a portion of liquid aliment, as a few spoonsful of soup, -were introduced into the stomach at the external orifice, the rugæ -(fig. CLXVII. 1) immediately closed gently upon it; gradually diffused -it through the gastric cavity, and prevented the entrance of a second -quantity till this diffusion was effected; then relaxation again took -place, and admitted of a further supply. When solid food was introduced -in the same manner, either in large pieces or finely divided, the same -gentle contraction and grasping motions were excited, and continued -from fifty to eighty seconds, so as to prevent more from being -introduced, without considerable force till the contraction was at an -end. - -651. When the position of the body was such that the cardiac portion -of the stomach was brought into view, and a morsel of food was -swallowed in the natural mode, a similar contraction of the stomach, -and closing of its fibres upon the bolus was invariably observed to -take place; and till this was over, a second morsel could not be -received without a considerable effort. Hence, in addition to the other -purposes accomplished by mastication, insalivation, and deglutition, -it is probable that these operations answer the further use of duly -regulating the time for the admission of successive portions of the -food into the stomach.[7] - - [7] See Dr. Andrew Combe on the Physiology of Digestion, in whose - work a full detail of this instructive case is given. See also Mayo’s - Outlines of Physiology, 4th Edit. Appendix. - -652. On watching the phenomena that take place on the contact of a -portion of food with the stomach, the circumstances described (627) -are seen; the change in the mucous coat from a pale pink to a deep red -colour, in consequence of the enlargement of the blood-vessels and -their admission of a greatly increased number of red particles; the -undulating motion of the stomach, in consequence of the contraction of -its muscular fibres, excited by the stimulus of food; the distillation -of the gastric juice from the enlarged and excited papillæ; the -continuous flow of this fluid until the complete solution of the food, -when food is present; and, on the contrary, the cessation of this -discharge in a short time when it is produced by a mechanical irritant, -as the bulb of a thermometer, although at first the gastric juice -distil from the papillæ, from the contact of such an irritant, just as -when excited by the contact of food. - -653. On collecting the gastric juice and placing it in contact with an -alimentary substance out of the stomach, its solution takes place more -slowly, but not less completely, than when retained in the stomach. -An ounce of this fluid was placed in a vial with a piece of boiled, -recently salted beef, weighing three drachms; the vial was then tightly -corked, and immersed in water, raised to the temperature of 100°, -previously ascertained to be the ordinary heat of the stomach. In forty -minutes the process of solution had commenced on the surface of the -beef. In fifty minutes the texture of the beef began to loosen and -separate. In sixty minutes an opaque and cloudy fluid was formed. In -one hour and a half the muscular fibres hung loose and unconnected, and -floated about in shreds in the more fluid matter. In three hours the -muscular fibres had diminished about one half. In five hours only a -few remained undissolved. In seven hours the muscular texture was no -longer apparent; and in nine hours the solution was completed. - -654. At the commencement of this experiment a piece of the same beef of -equal weight and size was suspended within the stomach by means of a -string. On examining this portion of beef at the end of half an hour, -it was found to present precisely the same appearance as the piece in -the vial; but on the removal of the string at the end of an hour and -a half the beef had been completely dissolved, and had disappeared, -making a difference of result in point of time of nearly seven hours. -In both, the solution began on the surface, and agitation accelerated -its progress by removing the external coating of chyme as fast as it -was formed. - -655. An ordinary dinner having been taken, consisting of boiled salted -beef, bread, potatoes, and turnips, with a gill of pure water for -drink, a portion of the contents of the stomach was drawn off into an -open mouthed vial, twenty minutes after the meal. The vial was placed -in a water-bath, maintained steadily at a temperature of 100°. It -was continued in this temperature for five hours. At the end of that -time the whole contents of the vial were dissolved. On comparing the -solution with an equal quantity of chyme taken from the stomach, little -difference could be distinguished between the two fluids, excepting -that it was manifest that the digestive process had proceeded somewhat -more rapidly in, than out of the stomach. The food, in this experiment, -after having remained in contact with the stomach for the space of -twenty minutes, had imbibed a sufficient quantity of gastric juice to -complete its solution. - -656. Fifteen minutes after half a pint of milk had been introduced into -the stomach, it presented the appearance of a fine loosely-coagulated -substance mixed with a semi-transparent whey-coloured fluid. A drachm -of warm gastric juice poured into two drachms of milk at a temperature -of 100°, produced a precisely similar appearance in twenty minutes. In -another experiment, when four ounces of bread were given with a pint of -milk, the milk was coagulated and the bread reduced to a soft pulp in -thirty minutes, and the whole was completely digested in two hours. - -657. When the albumen or white of two eggs was swallowed on an empty -stomach, small white flakes began to be seen in about ten or fifteen -minutes, and the mixture soon assumed an opaque whitish appearance. In -an hour and a half the whole had disappeared. Two drachms of albumen -mixed with two of gastric juice out of the stomach underwent precisely -the same changes, but in a somewhat longer time. - -658. Dr. Beaumont’s observations are adverse to the opinion, founded -on numerous experiments, that the food is arranged in the stomach in -a definite manner, and that a distinct line of separation exists -between old and new food (626). In the human stomach, according to -the subject of these experiments, the ordinary course and direction -of the food are first from right to left along the small arch, and -thence through the large curvature from left to right. The bolus as -it enters the cardia turns to the left, passes the aperture, descends -into the splenic extremity, and follows the great curvature towards the -pyloric end. It then returns in the course of the smaller curvature, -makes its appearance again at the aperture, in its descent into the -great curvature, to perform similar revolutions. These revolutions -are completed in from one to three minutes. They are probably induced -in a great measure by the circular or transverse muscles of the -stomach (615), as is indicated by the spiral motion of the stem of -the thermometer, both in descending to the pyloric portion, and in -ascending to the splenic. These motions are slower at first than -after chymification has considerably advanced. The whole contents -of the stomach, until chymification be nearly complete, exhibit a -heterogeneous mass of solids and fluids, hard and soft, coarse and -fine, crude and chymified; all intimately mixed, and circulating -promiscuously through the gastric cavity like the mixed contents of a -closed vessel, gently agitated or turned in the hand. - -659. In attempting to pass a long glass thermometer through the -aperture into the pyloric portion of the stomach, during the latter -stages of digestion, a forcible contraction is perceived at the point -of the hour-glass contraction of the stomach, and the bulb is stopped. -In a short time there is a gentle relaxation, when the bulb passes -without difficulty, and appears to be drawn quite forcibly, for three -or four inches, towards the pyloric end. It is then released, and -forced back, or suffered to rise again, at the same time giving to the -tube a circular or rather a spiral motion, and frequently revolving it -quite over. These motions are distinctly indicated and strongly felt -in holding the end of the tube between the thumb and finger; and it -requires a pretty forcible grasp to prevent it from slipping from the -hand, and being drawn suddenly down to the pyloric extremity. When the -tube is left to its own direction at these periods of contraction, it -is drawn in, nearly its whole length, to the depth of ten inches; and -when drawn back requires considerable force, and gives to the fingers -the sensation of a strong suction power, like drawing the piston from -an exhausted tube. This ceases as soon as the relaxation occurs, and -the tube rises again, of its own accord, three or four inches, when the -bulb seems to be obstructed from rising further; but if pulled up an -inch or two through the stricture, it moves freely in all directions -in the cardiac portions, and mostly inclines to the splenic extremity, -though not disposed to make its exit at the aperture. These peculiar -motions and contractions continue until the stomach is perfectly -empty, and not a particle of food or chyme remains, when all becomes -quiescent again. - -660. The chambers in which the remaining part of the digestive process -is carried on are much less accessible, and no such favourable -opportunity as that enjoyed by Dr. Beaumont has occurred of rendering -their operations manifest to the eye. Nevertheless, the researches of -physiologists have succeeded in disclosing, with almost equal exactness -and certainty, the successive changes which the food undergoes even in -these more hidden organs, that admit of no exposure during life without -extreme danger. - -661. The chyme on passing through the pylorus is received into a -chamber (fig. CLXVII. 3) which forms the first portion of the small -intestines. The small intestines, taken together, constitute a tube -about four times the length of the body. This tube is conical, the -base of the cone being towards the pylorus, and its apex at the valve -of the colon, where the small intestines terminate in the large. From -the pylorus to the valve of the colon the small intestines diminish in -capacity, in thickness, in vascularity, in the size of the villi, and -in the depth and number of the valvulæ conniventes. - -[Illustration: Fig. CLXXI. - - 1. Esophagus. 2. Stomach. 3. Liver raised, showing the under surface. - 4. Duodenum. 5. Small intestines, consisting of—6. Jejunum and ilium. - 7. Colon. 8. Urinary bladder. 9. Gall bladder. 10. Abdominal muscles - divided and reflected.] - -662. The first portion of the small intestine is termed the duodenum -(fig. CLXVII. 3). It is about twelve inches in length, and, unlike the -stomach, which is capable of considerable motion, it is closely tied -down to the back by the peritoneum, which imperfectly covers it. The -rest of the small intestine is divided into two portions—the upper -two-fifths of which are termed jejunum, and the three lower ilium. - -663. The duodenum, the chamber which receives the chyme from the -pylorus, is a second stomach, which carries on the process commenced -in the first. It is assisted in the performance of its function by two -organs of considerable magnitude, the pancreas and the liver. - -664. The pancreas is a conglomerate gland (fig. CLXXII. 5), of an -elongated form, placed in the epigastric region, lying transversely -across it, immediately behind the stomach (fig. CLXXII. 1), and resting -upon the spinal column (fig. CLXXII. 5). Its right extremity is -attached to the duodenum (fig. CLXXII. 9), and its left to the spleen -(fig. CLXXII. 4). In external appearance it resembles the salivary -glands, but it is of much larger size, and its weight, from four to six -ounces, is three times greater than that of all the salivary glands -together. It secretes a peculiar fluid called the pancreatic juice, -which is carried into the duodenum by a tube named the pancreatic duct -(fig. CLXVII. 7), which opens into the duodenum about four or five -inches from its pyloric end (fig. CLXVII. 2). - -[Illustration: Fig. CLXXII. - - 1. Stomach raised. 2. Under surface of liver. 3. Gall bladder. 4. - Spleen. 5. Pancreas. 6. Kidneys. 7. Ureters. 8. Urinary bladder. 9. - Portion of intestine called duodenum. 10. Portion of intestine called - rectum. 11. Aorta.] - -665. The liver, the largest and heaviest gland in the body, weighing -about four pounds, is placed chiefly in the right hypochondriac region -(fig. CLXXI. 3); but a portion of it extends transversely across the -epigastric, into the left hypochondriac region (figs. CV. and CVII. -3). Its upper surface is in contact with the diaphragm (fig. LX. 6, b); -its under surface with the pyloric extremity of the stomach (fig. LX. -7), and its margin can be felt under the edges of the ribs of the right -side. - -666. It has been stated (473, 1.) that the fluid secreted by the liver, -unlike that formed by any other organ of the body, is elaborated from -venous blood, derived from the veins of the digestive organs, and -that these veins uniting together, form a common trunk called the -vena portæ, which penetrates the liver and ramifies through it in the -manner of an artery. Galen long ago compared this venous system to a -tree whose roots are dispersed in the abdomen, and its branches spread -out through the liver. Two comparatively small arteries, called the -hepatic, nourish the liver; the ultimate divisions of these arteries -likewise terminate in the vena portæ. The ultimate branches of the -vena portæ terminate partly in a system of veins, called the hepatic, -which like ordinary veins return the blood to the right side of the -heart; and partly in a system of tubes, termed the biliary ducts, -which contain the fluid secreted by the capillary branches of the vena -portæ. This fluid is the bile. The biliary ducts uniting from all -parts of the liver by innumerable branches, at length form a single -trunk termed the hepatic duct (fig. CLXVII. 9), which carries the bile -partly to the gall bladder (fig. CLXVII. 8) by a duct called the -cystic (fig. CLXVII. 10), and partly to the duodenum (fig. CLXVII. 3) -by a duct named the choledoch (fig. CLXVII. 6), a common trunk formed -by the union of the cystic with the hepatic (fig. CLXVII. 10 and 9). -The choledoch duct opens into the duodenum at the same point as the -pancreatic (fig. CLXVII. 7), and generally by a common orifice. - -667. The duodenum, on receiving the chyme from the stomach, transmits -it slowly along its surface. The kind of motion by which the chyme is -borne along the surface of the duodenum is perfectly analogous to that -by which it is transmitted from the stomach to the duodenum, irregular, -sometimes in one direction, and sometimes in another, at one time -commencing in one part of the organ, at another time in another, always -slow, but ultimately progressive. - -668. As the chyme slowly advances through the upper part of the -duodenum, the biliary and the pancreatic juices slowly distil into -the lower portion of the organ. The bile is seen to exude from the -choledoch duct, not continually, but at intervals, a drop appearing at -the orifice, and diffusing itself over the neighbouring surface, about -twice in a minute, while the flow of the pancreatic juice is still -slower. - -669. No appreciable change takes place in the chyme until it reaches -the orifice of the choledoch duct; but as soon as it comes in contact -with this portion of the duodenum, the chyme suddenly loses its own -sensible properties, and acquires those of the bile, especially its -colour and bitterness. But these properties are not long retained; a -spontaneous change soon takes place in the compound. It separates into -a white fluid and into a yellow pulp. The white fluid is the nutritive -part of the aliment; the yellow pulp is the excrementitious matter. - -670. This white fluid, the proper product of the digestive process, -as far as it has yet advanced, is called chyle. If any portion of oil -or fat have been contained in the food, the chyle is of a milk-white -colour; if not, it is nearly transparent. It is of the consistence -of cream, and it bears a close resemblance to cream in its sensible -properties. It differs from chyme in being of a whiter colour, more -pellucid, and of a thicker consistence: it differs also in its chemical -nature, for, whereas chyme is acid, chyle is alkaline. - -671. Three fluids are mixed with the chyme in the duodenum, each of -which contributes to the conversion of the chyme into chyle. First, the -secretion of the duodenum itself, a solvent analogous to the gastric -juice. Secondly, the secretion of the pancreas, a watery fluid holding -in solution highly important principles, namely, a large quantity of -albumen, a matter resembling casein, osmazome, and different salts. -Thirdly, the secretion of the liver, a compound fluid, consisting of -water, mucus, and several peculiar animal matters, namely, resin, -cholesterine, picromel, cholic acid, a colouring matter, probably -salivary matter, osmazome, casein, and many salts. - -672. There cannot be a question that the secretion of the duodenum has -a solvent power over the chyme analogous to that of the gastric juice. -Some physiologists indeed maintain that the juice poured out from the -inner surface of the duodenum is as powerful a solvent as the gastric -juice. It is certain that substances which have escaped chymification -in the stomach undergo that process in the duodenum, and that there is -the closest analogy between the action of the duodenum on the chyme and -that of the stomach on the crude food. - -613. The pancreatic secretion adds to the chyme richly azotized animal -substances, albumen, casein, osmazome (671), by which it is brought -nearer the chemical composition of the blood, and prepared for its -complete assimilation into it. The first addition of such assimilative -matter, it has been shown, is communicated by the salivary glands, but -far more important additions are now supplied from the pancreas. Hence -the larger size of the pancreas and the more copious secretion of the -pancreatic fluid, in herbivorous than in carnivorous animals; hence the -change produced in the size of the pancreas by a long continued change -in the habits of an animal; hence the smaller size of the pancreas in -the wild cat, which lives wholly on animal food, than in the domestic -cat, which lives partly on animal and partly on vegetable food. - -674. The bile, the most complex secretion in the body, accomplishes -manifold purposes. - -1. Like the pancreatic secretion, it communicates to the chyle richly -azotized animal substances, picromel, osmazome, and cholic acid (671); -by the combination of which with the chyme, it is brought still nearer -the chemical composition of the blood. These principles are manifestly -united with the chylous portion of the chyme, since they are not -discoverable in its excrementitious matter. - -2. Bile has the property of dissolving fat; consequently, when oily -or fatty matters are contained in the food, it powerfully assists in -converting these substances into chyle. - -3. The excrementitious portion of the bile is highly stimulant. The -contact of its bitter resin with the mucous membrane of the intestines -excites the secretion of that membrane; hence the extreme dryness of -the excrementitious matter when the choledoch duct of an animal has -been tied; and hence the same dryness of this matter in jaundice, when -the bile, instead of being conveyed by its appropriate duct into the -duodenum, is taken up by the absorbents, poured into the blood, and -distributed over the system. - -4. The bitter resin of the bile stimulates to contraction the fibres -of the muscular tunic of the intestines: by the contraction of these -fibres the excrementitious matter is conveyed in due time out of the -body; hence the constipated state of the bowels invariably induced when -the secretion of the bile is deficient, or when its natural course into -the intestines is obstructed. - -5. The excrementitious portion of the bile exerts an antiseptic -influence over the excrementitious portion of the food during its -passage through the intestines. In animals in which the choledoch duct -has been tied, the excrementitious portion of the food is invariably -found much further advanced in decay than in the natural state. This -is also uniformly the case in the human body in proportion as the -secretion of the bile is deficient, or its passage to the intestine is -obstructed. - -675. Such appear to be the real purposes accomplished by the bile -in the process of digestion. Several uses have been assigned to -it, in promoting this process, which it does not serve. Seeing the -instantaneous change wrought in the chyme on its contact with the -bile, it was reasonable to suppose that the main use of the bile -was to convert chyme into chyle, a purpose apparently of sufficient -importance to account for the immense size of the gland constructed -for its elaboration. The soundness of this conclusion appeared to be -established by direct experiment. Mr. Brodie placed a ligature around -the choledoch duct of an animal: after the operation the animal ate -as usual: on killing the animal some time after it had taken a meal, -and examining the body immediately after death, it was clear that -chymification had gone on in the stomach just as when the choledoch -duct was sound, but no chyle appeared to be contained either in the -intestines or in the lacteals. In the lacteals there was found only a -transparent fluid, which was supposed to consist of lymph and of the -watery portion of the chyme. Mr. Brodie’s experiments seemed to be -confirmed by those of Mr. Mayo, who arrived at the conclusion, that -when the choledoch duct is tied, and the animal is examined at various -intervals after eating, no trace whatever of chyle is discoverable in -the lacteal vessels. But these experimentalists inferred that no chyle -existed in the intestines or lacteals, because there was present no -fluid of a milk-white colour, a colour not essential to chyle, but -dependent on the accident of oily or fatty matter having formed a -portion of the food. These experiments have been repeated in Germany -by Tiedemann and Gmelin, and in France by Leuret and Lassaigne, who -have invariably found, after tying the choledoch duct, nearly the same -chylous principles, with the exception of those derived from the bile, -as in animals perfectly sound; and the English physiologists have since -admitted that their German and French colaborateurs have arrived at -conclusions more correct than their own. - -676. The bile consists then of two different portions; a highly -animalized portion, which combines with the chyme and exalts its -nature by approximating it to the condition of the blood; and an -excrementitious portion, which, after accomplishing certain specific -uses, is carried out of the system with the undigested matter of the -food. The excrementitious portion of the bile, namely, the resin, the -fat, the colouring principle, the mucus, the salts, constitute by far -the largest portion of it. These constituents of the bile for the most -part contain a very large proportion of carbon and hydrogen, and the -reasons have been already fully stated (473, _et seq._) which favour -the conclusion that the elimination of these substances under the form -of bile is one most important mode of maintaining the purity of the -blood, and that the liver is thus a proper respiratory organ, truly -auxiliary to the lungs. It is a beautiful arrangement, and like one -of the adjustments of nature, that the bile, the formation of which -abstracts from the blood so large a portion of carbon and hydrogen as -to maintain the purity of the circulating mass and to counteract its -putrescent tendency, acts on the excrementitious portion of the food, -always highly putrescent, as a direct and powerful antiseptic; that -the very matter which is eliminated on account of the putrid taint -it communicates to the blood, on its passage out of the body, stops -the putrefaction of the substances which have been ministering to the -replenishment of the blood. - -677. The chyle, thick, glutinous, and adhesive, attaches itself -with some degree of tenacity to the mucous surface of the duodenum. -Nevertheless, by the successive contractions of the muscular fibres of -the duodenum the fluid is slowly but progressively propelled forwards. -The separation of the excrementitious matter becomes more complete, -and consequently the chyle more pure as it advances, until, having -traversed the course of the duodenum, it enters the second portion of -the small intestines, the jejunum. - -678. The jejunum, so called because it is commonly found empty, and the -ilium, named from the number of its convolutions, on account of their -great length, are provided with a distinct membrane to support them, -and to retain them in their situation, termed the mesentery. - -679. The mesentery is a broad membrane composed of two layers of -peritoneum. Between these two layers, at one extremity of the -duplicature, is placed the intestines, while the other extremity is -attached to the spinal column. The mesentery being much shorter than -the intestines, the intestines are gathered or puckered upon the -membrane, by which beautiful mechanical contrivance they are held in -firm and close contact with each other, yet their convolutions cannot -be entangled, nor can they be shaken from their place by the sudden -and often violent movements of the body. It sometimes happens, in -consequence of disease, that the convolutions of the intestines are -glued together by the effusion of lymph, and then the most trifling -causes are capable of producing the severest symptoms of obstruction in -the bowels. - -680. The internal surface of the small intestines is distinguished, - -1. By the number of the mucous glands, which may be seen by a -magnifying glass to consist partly of a prodigious number of the -minutest follicles, not collected in groups, but equally scattered -throughout; and partly of glands of a larger dimension, disposed in -groups at particular parts of the canal. - -2. By the increase in the number and size of the villi, of which there -are about four thousand to the surface of a square inch. Like those of -the stomach, the villi of the small intestine are composed of arteries, -veins, nerves, and mucous ducts; but to the villi of the small -intestine, in length about one-fourth of a line, there is added a new -vessel, the absorbent of the chyle, the lacteal (figs. 175 and 176), so -named from the milk-like chylous fluid which it contains. - -3. By the great extension of the mucous coat obtained by the -disposition of the membrane into the folds called valvulæ conniventes -(fig. CLXXIII.). These folds, which rarely extend through the whole -circle of the intestine, are often joined by communicating folds (fig. -CLXXIII.). The folds are broadest in the middle, and narrowest at the -extremities (fig. CLXXIII.). In general, they are about a line and a -half broad. One edge of the fold is loose, but the other is fixed to -the intestine (fig. CLXXIII.). The office of these folds is, first, -without increasing space, to extend surface for the distribution of the -villi; and, secondly, to retard the flow of the chyle, by opposing to -its descent valves so constructed and disposed as, without arresting -its progress, to moderate and regulate its course, in order that time -may be allowed for its absorption. - -[Illustration: Fig. CLXXIII. - - Internal view of a portion of the jejunum, showing the arrangement of - the mucous membrane into valvulæ conniventes.] - -[Illustration: Fig. CLXXIV.—_View of the Outer Coats of the Small -Intestine._ - - 1. Peritoneal coat reflected off. 2. Muscular Coat consisting of—_a._ - longitudinal fibres. _b._ Circular fibres.] - -681. The onward flow of the chyle through the course of the small -intestines is effected by the action of the double layer of muscular -fibres, the circular and the longitudinal fasciculi which compose -its muscular coat (fig. CLXXIV.). The disposition of the muscular -fibres of the alimentary canal in general, and of this part of it in -particular, deserves special notice. The ordinary arrangement and -action of muscular fibres would not have produced in this case the kind -and degree of motion required. The muscular fibres that compose the -ventricles of the heart are so accumulated and disposed, that their -contraction originates, and communicates energetic impulse. The muscles -of the arm are so accumulated and disposed that their contraction -originates the like energetic impulse. Muscles so accumulated in the -alimentary canal would have produced motion, indeed, but motion not -only not accomplishing the end in view, but directly defeating it. In -order to obtain the kind and degree of motion in this case required, -the firm and thick muscle is attenuated into minute, delicate, and -thready fibres, not concentrated in a bulky mass, so as to obtain by -their accumulation a great degree of force; but spread out in such -a manner as to form a thin and almost transparent coat. The tender -fibres composing this delicate coat, by their contraction, produce two -alternate, gentle, almost constant motions, called the peristaltic, -from its resemblance to the motion of the earth-worm, and the -antiperistaltic. By the peristaltic action motion is begun at once in -several parts of the canal. Whenever the chyle is applied in a certain -quantity to any part of the intestines, that part contracts, and makes -a firm point, towards which the portions both above and below are -drawn, by means of the longitudinal fibres which shorten the canal, and -at the same time dilate the under part. By the antiperistaltic action, -which is the exact reverse of the former, the chyle is turned over and -over, and exposed to the orifices of the lacteal vessels; while, by the -motion of the chyle forwards and backwards, and backwards and forwards, -produced by these two actions constantly alternating with each other, -its slow, gentle, but ultimately progressive course is secured. - -682. The chyle thus gently moved along the extended surface of the -jejunum and ilium, and still in its course acted upon in some degree -by the secretions poured out upon the mucous membrane, successively -disappears, until at the termination of the ilium (fig. CLXXI. 5) there -is scarcely any portion of it to be perceived. It is taken up by the -vessels termed lacteals. - -683. The lacteal vessels (figs. 175 and 176), take their origin on -the surface of the villi, by open mouths, too minute to be visible -to the naked eye, but distinguishable under the microscope. These -minute, pellucid tubes, wholly countless in number, are composed of -membranous coats so thin and transparent that the milky colour of their -contents, from which they derive their name, is visible through them, -and yet they are firm and strong. They present a jointed appearance -(figs. CLXXVI. 4, and CLXXVII. 7). Each joint denotes the situation -of the valves with which they are provided, and which are placed at -regular distances along their entire course (fig. CXCII. 1 and 2). -These valves, which are generally placed in pairs (fig. CXCII. 2), -consist of a delicate fold of membrane of a semilunar form, one edge of -which is fixed to the side of the vessel, while the other lies loose -across its cavity (fig. CXCII. 2). So firm is this membrane, and so -accurately does it perform the office of a valve, that even after death -it is capable of supporting a column of mercury of considerable weight -without giving way, and of preventing a retrograde course of the fluid. -The lacteals are nourished by blood-vessels, and animated by nerves, -and it is conceived that they must be provided with muscular fibres, or -some analogous tissue, for they are obviously contractile, and it is -by this contractile power that their contents are moved. The delicacy -and transparency of the vessels, however, render it impossible to -distinguish the different tissues which compose their walls. - -[Illustration: Fig. CLXXV. - - View of the inner surface of the ilium as it appears some hours after - a meal. 1. The smaller branches of the lacteals, turgid with chyle, - covering the surface of the intestine. 2. Larger branches of the - lacteals formed by the union of the smaller branches.] - -[Illustration: Fig. CLXXVI. _View of the course of the Lacteals._ - - 1. The aorta. 2. Thoracic duct. 3. External surface of a portion of - small intestine. 4. Lacteals appearing on the external surface of - the intestine after having perforated all its coats. 5. Mesenteric - glands of the first order. 6. Mesenteric glands of the second order. - 7. Receptacle for the chyle. 8. Lymphatic vessels terminating in the - receptacle of the chyle, or commencement of the thoracic duct.] - -684. If the mucous coat of the small intestines be examined some hours -after a meal, the lacteals are seen turgid with chyle, covering its -entire surface (fig. CLXXV. 1). These vessels, which are sometimes -of such magnitude and in such numbers as entirely to conceal the -ramifications of the blood-vessels, unite freely with each other, and -form a net-work, from the meshes of which proceed branches which, -successively uniting, form branches of a larger size (fig. CLXXV. 2). -These larger branches perforate the mucous coat and pass for some way -between the mucous and the muscular tunics: at length they perforate -both the muscular and the peritoneal coats, when, from having been -on the inside of the intestine, they get on the outside of it (fig. -CLXXVI. 3, 4), and are included, like the intestine itself, between the -layers of the mesentery. All the different sets of lacteals converging -and uniting together, form an exceedingly complicated plexus of vessels -within the fold of the mesentery. Radiating from this plexus, the -lacteals advance forwards until they reach the glands, called, from -their being placed between the fold of the mesentery, the mesenteric -(figs. CLXXVI. 5 and 6, and clxxvii. 2 and 3); rounded, oval, -pale-coloured bodies, consisting of two sets, arranged in a double -row (figs. CLXXVI. 5 and 6, and CLXXVII. 2 and 3); the set nearest -the intestine (fig. CLXXVII. 2) being considerably smaller than the -succeeding set (fig. CLXXVII. 3). - -[Illustration: Fig. CLXXVII. - - View of the course of the Thoracic Duct from its origin to its - termination. 1. Lacteal vessels emerging from the mucous surface of - the intestines. 2. First order of mesenteric glands. 3. Second order - of mesenteric glands. 4. The great trunks of the lacteals emerging - from the mesenteric glands, and pouring their contents into—5. The - receptacle of the chyle. 6. The great trunks of the lymphatic or - general absorbent system terminating in the receptacle of the chyle. - 7. The thoracic duct. 8. Termination of the thoracic duct at—9. The - angle formed by the union of the internal jugular vein with the - subclavian vein.] - - -685. On reaching the first series of glands (fig. clxxvii. 2), the -lacteals penetrate the substance of the gland, in the interior of -which they communicate with each other so freely, and form such -innumerable windings, that the gland seems to consist of a congeries -of convoluted lacteals. Emerging from the first series of glands, the -lacteals proceed on their course to the second series (fig., CLXXVII. -3), which they penetrate, and in the interior of which they present -the same convoluted appearance as in the first set. On passing out of -this second series of glands, the lacteals unite together, and compose -successively larger and larger branches, until at length they form two -or three trunks (fig. CLXXVII. 4), which terminate in the small oval -sac (fig. CLXXVII. 5), termed the receptacle of the chyle (receptaculum -chyli). - -686. In this oval sac or receptacle of the chyle (fig. CLXXVII. -5), which rests upon the second or the first lumbar vertebra, also -terminate the trunks of the general absorbent vessels of the system -(fig. clxxvii. 6), called from the _lymph_ or the pellucid fluid which -they contain, lymphatics, as the lacteals are named from the lactitious -or milky appearance of their contents. - -687. The receptacle of the chyle produced forms the thoracic duct -(fig. CLXXVII. 7), a canal about three lines in diameter. This tube -rests upon the spinal column, ascends on the right side of the aorta, -passes through the aortic opening in the diaphragm (fig. CXXXIV. 9, -10), and enters into the chest. Here it forms a transparent tube about -the size of a crow-quill; it rests upon the bodies of the dorsal -vertebræ; it continues to ascend still on the right side of the aorta, -until it reaches the sixth or fifth dorsal vertebra, when changing its -direction, it passes obliquely over to the left side (fig. CLXXVII. 7). -From this point it continues its course upwards, on the left side of -the neck, as high as the sixth cervical vertebra; when suddenly turning -forwards and a little downwards, it terminates its course in the angle -formed by the union of the internal jugular with the subclavian vein -(fig. CLXXVII. 8, 9). At its termination in these great venous trunks -are placed two valves, which prevent alike the return of the chyle, and -the entrance of the blood into the duct (fig. CLXXVIII.). - -[Illustration: Fig. CLXXVIII.—_Valve at the termination of the Thoracic -Duct._ - - 1. The Thoracic Duct. 2. Lymphatics entering the duct. 3. The vein - laid open, showing the valve at the termination of the duct. 4. The - left internal jugular vein. 5. The left subclavian vein. 6. The vein - called innominata. formed by the union of the internal jugular and - subclavian veins. 7. The right jugular vein. 8. The right subclavian - vein. 9. The superior cava formed by the union of the veins above. 10. - The inferior cava formed by the union of the veins below. 11. The two - venæ cavæ passing to the right auricle of the heart. 12. The heart. - 13. The pulmonary artery dividing into right and left branches. 14. - The aorta.] - -688. This account of the course of the thoracic duct is a description -of the course of the chyle. Performing a double, circuitous, and -slow circulation through the minute convoluted tubes of which the -double series of mesenteric glands are composed, the chyle, in its -receptaculum, is mixed with the contents of the lymphatic vessels, -lymph (fig. CLXXVII. 6, 5), that is, organic matter brought from every -surface and tissue of the body. Both fluids, chyle and lymph, mixed and -mingled, flow together into the thoracic duct, by which in the course -traced (687) they are poured into the blood, just as the venous torrent -is rushing to the heart (fig. CLXXVIII. 6, 9, 11). - -689. Thus, the final product of digestion, the chyle; particles of -organized matter, the lymph; and venous blood, that is, blood which has -already circulated through the system commingled, flow together to the -right heart, by which it is transmitted to the lungs, where all these -different fluids are converted into one substance, arterial blood, to -be by the left heart sent out to the system for its support. - -690. While these processes are going on, another and a very important -function is performed by the remaining portion of the alimentary canal. -It is the office of this part of the apparatus to carry out of the body -that portion of the aliment which is incapable of being converted into -chyle. The preparation of the excrementitious part of the aliment for -its expulsion constitutes the process of fecation. The organs in which -this process is carried on, and by which the excrementitious matter, -when duly prepared for its removal, is conveyed from the body, are the -large intestines. - -691. The large intestines (fig. CLXXIX.) consist of the cæcum, the -colon and the rectum (fig. CLXXIX.). The cæcum varies in length from -two inches to six; the colon is about five feet in length, and the -rectum is about eight inches. - -692. The ilium opens into the cæcum (fig. CLXXIX. 8, 10), just as the -esophagus opens into the stomach. At this point the ilium is elongated, -forming two concentric folds which join at their horns, and between -the folds are placed a number of muscular fibres. In this manner is -constructed a valve, which is termed the valve of the colon. It is -placed in a transverse direction across the intestine, and its action -as a valve is very complete. It admits of the free passage of the -contents of the small intestines into the large, but it prevents the -return of any portion of the contents of the latter into the former. - -[Illustration: Fig. CLXXIX.—_View of the Abdominal Portion of the -Digestive Organs._ - - 1. Esophagus. 2. Stomach. 3. Spleen. 4. Liver. 5. Gall-bladder - with its ducts. 6. Pancreas with its duct. 7. Duodenum. 8. Small - intestines. 9. Large intestines dividing into—10. Cæcum. 11. Ascending - colon. 12. Arch of the colon. 13. Descending colon. 14. Sigmoid - flexure here imperfectly represented. 15. Rectum.] - -[Illustration: Fig. CLXXX. - - Portion of the large intestine, showing the arrangement of the - muscular fibres. 1. The longitudinal fibres collected into bands, and - forming larger fasciculi. 2. The circular fibres arranged as in the - other intestines.] - -693. The colon is distinguished by its capacious size, its great -length, and its longitudinal bands, which consist of strong muscular -fasciculi (fig. CLXXIX. 11). It is divided into an ascending portion -which occupies the right iliac and hypochondriac regions (fig. CLXXIX. -11); the transverse portion, called its arch, which is placed directly -across the epigastric region (fig. CLXXIX. 12), a descending portion -which occupies the left hypochondriac region (fig. CLXXIX. 13), and a -fourth portion, which being curved somewhat like the italic letter S, -is called the sigmoid flexure, which occupies the left iliac region -(fig. CLXXIX. 14). The sigmoid flexure terminates in the last portion -of the alimentary canal, called the rectum (fig. CLXXIX. 15), which is -placed in the hollow of the sacrum, and which follows the curvature -of that bone (fig. XLV. 5). The circular fibres of the rectum are -accumulated at the termination of the bowel to form the internal -sphincter of the anus. External to this is placed another set of -fibres, which constitute the external sphincter. - -694. The mucous membrane of the large intestines is disposed -differently from that of the small intestines, and the mucous membrane -of the colon still differently from that of the rectum. In the colon -the mucous membrane, instead of being disposed in the form of valvulæ -conniventes, is so arranged as to divide its whole surface into -minute apartments or cells by which the descent of the fecal matter -is retarded still more than the descent of the chyle by the valvulæ -conniventes. Some particles of chyle do, however, continue to be -separated from the fecal matter, even in the large intestines; and in -order that nothing may be lost, a few valvulæ conniventes, with their -lacteals, appear here also, while the cells of the colon, by retarding -the descent of the fecal matter, allow time for the more complete -separation and absorption of the chylous particles. - -695. In the rectum the mucous membrane is plaited into large transverse -folds, which disappear as the fecal matter descends into the bowel, -accumulates in it, and distends it; an arrangement which gives to this -portion of the intestine its power of distension, so closely connected -with our convenience and comfort. - -696. As soon as that portion of the alimentary matter which is -transmitted to the large intestines reaches the colon it ceases to -be alkaline, the distinctive character of the contents of the small -intestines, and becomes acid, just as the whole alimentary mass is -acid at the commencement of digestion in the stomach. It acquires -albumen; its gases are no longer the same, for whereas pure hydrogen -is contained in the small intestines, none is ever found in the large, -but in the place of it, carbureted and sulphureted hydrogen; and now -for the first time it receives its peculiar odour. As it continues -to descend, its fluid parts are progressively absorbed, so that it -becomes more and more solid, until it reaches the rectum, when it is -almost dry. Here the accumulation of it goes on to a considerable -extent, the peristaltic action at first excited by the distension of -the rectum being, it would appear, counteracted by the contraction -of the external sphincter of the anus. When, however, the distension -of the bowel reaches a certain point, it produces a sensation which -leads to the desire to expel its contents. The bowel is now thrown -into action by an effort of the will, and that action is powerfully -assisted by the descent of the diaphragm and the contraction of the -abdominal muscles, actions also induced by an effort of the will. Thus -the action of the first part of the digestive apparatus, that which is -connected with the reception and partly with the deglutition of the -food, is attended with consciousness, and is placed under the control -of the will; the main portion of the digestive apparatus, that in -which the essential part of the digestive process is carried on, is -without consciousness, and is placed beyond the influence of volition; -the last portion of the digestive apparatus, that connected with the -expulsion of the non-nutrient portion of the aliment, again acquires -sensibility and consciousness, and is placed under the control of the -will. The striking differences in the arrangement of the muscular -fibres in these different parts of the apparatus, in accordance with -the widely different function performed by them; the powerful muscles -connected with the prehension, mastication and deglutition of the food; -the delicate and transparent tissue of fibres forming the muscular -coat of the stomach and small intestines; the increase in the number -and strength of the fibres of the large intestines, and the prodigious -accession to them in the rectum, are adjustments not only exquisite and -admirable in their own nature, but so indispensable to our well-being -and comfort, that were the appropriate action of either to be suspended -but for a short period, life would be extinguished, or if it could be -protracted, it would be changed into a state of unbearable torment. - -697. From the preceding account of the structure and action of the -apparatus of digestion, on a comparison of all the phenomena, it -appears that the successive stages of the process are marked by the -progressive approximation of the food to the nature of the blood. The -main constituents, of the blood are albumen, fibrin, an oily principle, -and red particles. Even in the chyme there are traces of albumen, with -globules, not indeed to be compared in number with the red particles -of the blood, smaller in size, and without colour, but still of an -analogous nature. In the chyle of the duodenum the quantity of albumen -is larger, there are traces of fibrin, and of an oily matter, and the -number of the globules is increased. In the chyle, after its exit from -the mesenteric glands, the albumen, the fibrin, the oil, the globules, -and more especially the two first and the last, are greatly increased. -But in the chyle when it reaches the thoracic duct, these principles -are so augmented, concentrated, and approximated to the state in which -they exist in the blood, that the chyle is now capable of undergoing -the characteristic process of the blood; for as the blood, when drawn -from a vein, undergoes spontaneous coagulation, so the chyle, when -drawn from the thoracic duct, separates into three parts; a solid -substance or clot, which remains at the bottom of the vessel; a fluid -which surrounds the clot; and a thin layer of matter, which is spread -over the surface of the fluid. The solid substance is analogous to the -fibrin, and the fluid to the serum of the blood; while the layer of -matter which is spread over the fluid is of an oily nature: moreover, -the chyle, when in contact with the air, quickly changes to a red -colour, and abounds with minute particles of various sizes, but the -largest of which is not yet equal to the diameter of the red particles -of the blood. - -698. The changes wrought upon the food, by which it is thus -approximated to the chemical composition of the blood, are effected, -as has been shown, partly by the gastric and intestinal juices, and -partly by matters combined with the food highly animalized in their -own nature, and endowed with assimilative properties, as the salivary -secretion mixed with the food during mastication; the pancreatic -and biliary secretions mixed with the food during the conversion of -the chyme into chyle; and the mesenteric secretions mixed with the -elaborated chyle of the mesenteric glands, and lastly, organized -particles which have already formed a part of the living structures of -the body mixed with the chyle under the form of lymph in the thoracic -duct. - -699. The lymph, until lately regarded as excrementitious, is really -highly animalized, partly combined with the chyle as its last and -highest assimilative matter; whence the compound formed by the -admixture of chyle and lymph is far more proximate to the blood than -the purest and most concentrated chyle; and partly returning with the -chyle to the lungs, to receive there a second depuration, and thereby a -higher elaboration. - -700. There is evidence that there is a series of organs specially -provided for the elaboration of the lymph no less than of the chyle. -There are organs manifestly connected with the digestive apparatus, -to which physiologists have found it extremely difficult to assign a -specific office. These organs have a structure in some essential points -alike; that structure is strikingly analogous to the organization of -glands: like glands, they receive a prodigious quantity of arterial -blood, and are supplied with a proportionate number of organic nerves; -yet they are without an excretory duct. The organs in question are -the bodies called the renal capsules, placed above the kidneys; the -thyroid and thymus glands situated in the neck, and the spleen in close -connexion with the stomach. - -701. These organs, however analogous in structure to glands, cannot, -it has been argued, be secreting organs, because they are destitute of -an excretory duct, do not manifestly form from the blood any peculiar -secretion, or, if they do, since there are no means of detecting -where it is conveyed, it is impossible to understand how it is -appropriated. But if these organs collect, concentrate, and elaborate -lymph, preparatory to its admixture with the chyle and to its being -sent a second time into the blood to undergo a second process of -depuration, they perform the function of glands; and their want of an -excretory duct, which has hitherto rendered their office so obscure, is -accounted for; they do not need distinct tubes for the transmission of -any product of secretion; the lymphatic vessels which proceed from them -and which convey the fluid they elaborate into the receptacle of the -chyle, are their excretory ducts. That one of these organs, the spleen, -is specially connected with the elaboration of the lymph, is manifest, -both from its chemical nature and from the remarkable change which -takes place in the chyle the moment the lymph from the spleen is mixed -with it. Tiedemann and Gmelin state, as the uniform result of their -observations and experiments, that the quantity of fibrin contained -in the chyle is greatly increased, and that it actually acquires red -particles as soon as the lymph from the spleen is mixed with it, and -that the lymph from the spleen superabounds both with fibrin and with -red particles. That the organs just enumerated, with the spleen, -perform a similar function, is inferred from their being, like it, of a -glandular structure, and without any excretory duct. If the spleen be -really one of a circle of organs appropriated to a function such as is -here supposed, a purpose is assigned to it adequate to its rank in the -scale of organization; inferior to few, if its importance be estimated -by the quantity of arterial blood with which it is supplied; yet this -is the organ for which Paley could find no better use than that of -serving for package. - -702. But in whatever mode the lymph be elaborated, it is certain that -it consists of matter highly animalized, and that its most important -principles, its albumen, its fibrin, its globules, and even its salts, -are in a chemical condition closely resembling that in which they exist -in the blood. - -703. It will appear hereafter that all the proximate principles of -which the body is composed are reducible by analysis to three, namely, -sugar, oil, and albumen: of these, sugar and oil are the least, and -albumen the most highly organized. Every alimentary substance must -contain at least one of these proximate principles, and in the various -articles which compose an ordinary meal always two, and often all -three, are afforded in abundance. From the phenomena which have been -stated, it is clear that the digestive organs, in acting on these -principles, exert the following powers. - -1. A solvent power. The first action of the stomach on the alimentary -substances presented to it is to reduce them to a fluid state. No -substance is nutritious which is not a fluid, or capable of being -reduced to a fluid. The stomach reduces alimentary substances to -a fluid state by combining them with water. Water enters into the -composition of organized bodies in two states, as an essential and -as an accidental element. A quantity of water is contained in sugar -when reduced to its dryest state; this water cannot be dissipated -without the decomposition of the sugar; it is therefore an essential -constituent of the compound. Water is combined with sugar in its -moist state: of this water much may be removed without destroying the -essential properties of the sugar: this part of the water is therefore -said to be an accidental constituent of the sugar. In most cases -organized bodies contain water in both these forms; and though it is -commonly impossible to discriminate between the water that is essential -and that which is accidental, yet the mode of union among the elements -of bodies in these two states of their combination with water are -essentially different. The stomach has the power of combining water -with alimentary substances in both these forms. Thus fluid albumen, -or white of egg, presented to the stomach is immediately coagulated -or converted into a solid. Soon this solid begins to be softened, and -the softening goes on until it is again reduced to a fluid. What was -fluid albumen in the white of egg is now fluid albumen in chyme; but -the albumen has undergone a remarkable change. Out of the stomach the -albumen of the egg may be converted by heat into a firm solid; but the -albumen of the chyme is capable of being converted only into a loose -and tender solid. In passing from its state in the egg to its state -in the chyme, the albumen has combined with a portion of water which -has entered as an essential ingredient into its composition. By this -combination the compound is reduced from what may be called a strong -to a weak state. This is the first action exerted by the stomach on -most alimentary substances. They are changed from a concentrated to a -diluted, from a strong to a weak state: the power by which the stomach -effects this change is called its reducing power, and the agent by -which it accomplishes it is the gastric juice; the essential ingredient -of which has been shown to be muriatic acid, or chlorine (639, _et -seq._). The muriatic acid obtained from the common salt of the blood -is poured in the form of gastric juice into the stomach, dissolves the -food, combines it with water, reduces it from a concentrated solid to -a dilute fluid; and thus brings it into the condition proper for the -subsequent part of the process. - -2. A converting power. Since whatever be the varieties of food, the -chyme invariably forms a homogeneous fluid, the stomach must be endowed -with the power of transforming the simple alimentary principles into -one another; the saccharine into the oily, and the oily into the -albuminous. The transformation of the saccharine into the oleaginous -principle is traceable out of the body in the conversion of sugar into -alcohol, which is essentially an oil. That the same transformation -takes place within the body is indubitable. The oleagenous and the -albuminous principles are already so nearly allied in nature to animal -substance that they do not need to undergo any essential change in -their composition. - -3. A completing power. When the alimentary substances have been reduced -and formed into chyme, when the chyme has been converted into chyle, -and when the chyle absorbed by the lacteals is transmitted to the -mesenteric glands, it undergoes during its passage through these organs -a process the direct reverse of that to which it is subjected in the -stomach; for whereas it is the office of the stomach to combine the -alimentary substances with water, it is one office of the mesenteric -glands to remove the superfluous water of the chyle; to abstract -whatever particles of matter may be contained in the compound which are -not indispensable to it, and to concentrate its essential constituents; -and consequently these organs exert on the digested aliment a -completing, in contradistinction to a reducing power. - -4. A vitalizing power. When sugar is converted into oil, when oil is -converted into albumen, when albumen, by the successive processes -to which it is subjected is completed, that is, when the alimentary -substances are made to approximate in the closest possible degree to -the nature of animal substance, they must undergo a still further -change, more wonderful than any of the preceding, and far more -inscrutible; they must be endowed with vitality; must be changed from -dead into living matter. Living substance only is capable of forming -a constituent part of living substance. The ultimate action of the -digestive organs is the communication of life to the food, to which -last and crowning process the reducing, converting, and completing -processes are merely subordinate and preparatory. Of the agency by -which this process is effected we are wholly ignorant; we know that -it goes on; but the mode in which it is accomplished is veiled in -inscrutable darkness. - -704. Blood is alive; blood is formed from the food; life is -communicated to the food before it is mixed with the blood. The blood -is essentially albumen, which it contains in the form of albumen -properly so called, in that of fibrin, and in that of red particles. -In the thoracic duct the strong albumen of the lymph is mixed with -the weaker albumen of the chyle. At the point where the thoracic duct -terminates in the venous system, lymph and chyle are mixed with venous -blood, and all commingled are borne directly to the lungs. There the -carbon with which the venous blood is loaded is expelled in the form -of carbonic acid gas; the particles of the lymph undergo some, as yet, -unknown change, exalting their organization; and the water hitherto -held in chemical union with the weak albumen of the chyle, is separated -and carried out of the system together with the carbonic acid gas in -the form of aqueous vapour. By this removal of its aqueous particles -the ultimate completion is given to the digested aliment; and the weak -and delicate albumen of the chyle is converted into the strong and firm -albumen of the blood. - -705. It has been stated (539), that though gelatin enters abundantly -into the composition of many tissues of the body, and performs most -important uses in the economy, it is never found in the blood; that -it is formed from the albumen of the blood by a reducing process, in -consequence of which carbon is evolved, which unites with the free -oxygen of the blood, forming carbonic acid, thus conducing, among other -purposes, to the production of animal heat. It is equally remarkable, -that though the lymphatics or absorbents arise in countless numbers -from every tissue of the body, and are endowed with the power of taking -up every constituent particle of every organ, solid as well as fluid, -yet gelatin is never found in the lymphatic vessels. The lymphatics -contain only albumen in a form far more proximate to the blood than -that of the chyle; consequently, before the gelatin of the body is -taken up by the lymphatics, it must be reconverted into albumen; that -is, the absorbed gelatin must undergo a process analogous to that which -gelatin and other matters undergo in the stomach and duodenum; it -follows that the digestive process is not confined to the stomach and -duodenum, but is carried on at every point of the body. Hence there are -two processes of digestion, a crude and a refined process. The crude -process is carried on in the stomach and duodenum, in which dead animal -matter is converted into living substance, as yet, however, possessing -only the lowest kind of vitality. The capillary arteries receiving the -substance thus prepared for them, build it up into structure perhaps -the lowest and coarsest, the least organized, and capable of performing -only the inferior functions. - -706. Capillary arteries in countless numbers terminate in the tissues -in membraneless canals (304 and 310). Particles of the blood are seen -to quit the arterial stream and to enter into the tissues, becoming a -component part of them: other particles are seen to quit the tissues -and to enter the current of the blood. The latter are probably organic -particles, to which a certain degree of elaboration has been already -given, now transmitted to the capillary veins, to be carried back to -the lungs to undergo there a further depuration, fitting them on their -return to the system for a higher organization. - -707. Thus the lymphatic vessels, analogous in so many other respects -to the veins, are probably similar to them in this also—that they take -up from the tissues particles already organized, in order to submit -them to processes which communicate to them a progressively higher -organization. The notion that the contents of the lymphatics consist of -worn-out particles, capable of accomplishing no further purpose in the -economy, is not tenable:— - -1. Because it is not analogous to the ordinary operations of nature to -mix wholly excrementitious matter with a substance for the production, -elaboration, and perfection of which, she has constructed such an -expensive apparatus. - -2. Because, on the other hand, the admixture of matter already highly -animalized with matter, as yet but imperfectly animalized, exalts the -nature of the latter, and is conducive to its complete animalization. - -3. Because the lymph, almost wholly albuminous, is already closely -allied in nature to the blood; it is, therefore, reasonable to infer, -that it is matter passing through an advancing stage of purification -and exaltation. - -4. Because this plan of progressive organization is in harmony with the -ordinary operations of nature, in which there is traceable a successive -ascent from the low to the high, the former being preparatory and -necessary to the latter. The tender and delicate organs of animal life, -the brain, the nerves, the apparatus of sense, the muscles, inasmuch as -they perform the highest functions, probably require to be constructed -of a more highly organized material, for the production of which the -matter primarily derived from crude aliment is subjected to different -processes, rising one above the other in delicacy and refinement; by -each of which it is made successively more and more perfect, until it -acquires the highest qualities of living substance, and is capable of -becoming the instrument of performing its most exalted functions. - - - - -CHAPTER XI. - -OF SECRETION. - - Nature of the function—Why involved in obscurity—Basis of the - apparatus consists of membrane—Arrangement of membrane into elementary - secreting bodies—Cryptæ, follicles, cæca and tubuli—Primary - combinations of elementary bodies to form compound organs—Relation of - the primary secreting organs to the blood-vessels and nerves—Glands - simple and compound—Their structure and office—Development of glands - from their simplest form in the lowest animals to their most complex - form in the highest animals—Development in the embryo—Number and - distribution of the secreting organs—How secreting organs act upon - the blood—Degree in which the products of secretion agree with, and - differ from, the blood—Modes in which modifications of the secreting - apparatus influence the products of secretion—Vital agent by which the - function is controlled—Physical agent by which it is effected. - - -708. Secretion is the function by which a substance, gaseous, liquid, -or solid, is separated or formed from the nutritive fluid. It is a -function as necessary to the plant as to the animal, and indispensable -alike to the life of both. It is of equal importance to the -preservation of the individual and to the perpetuation of the species. -In all living beings secretions are separated from the nutritive fluid, -and added to the aliment to assist in converting it into nutriment, -and are separated from the nutriment to maintain the composition of -the nutritive mass in a state fit for the continued performance of the -act of nutrition, and to form the germ on the development of which the -continuance of the species depends. - -709. The secretions of the plant, varied and abundant, are -indispensable to its nourishment, growth, and fructification. The -secretions of the animal more diversified, and far more constantly -performed, increase in number and elaborateness in proportion to -the range and intensity of the vital endowments and actions. In all -animals high in the scale of organization, and especially in man, the -products of secretion are vast in number, and exceedingly complex in -nature,—membrane, muscle, brain, bone;—the skin, the fat, the nail, -the hair;—water, milk, bile, wax, saliva, gastric juice;—whatever -substances enter as constituents into the corporeal structure;—whatever -substances are specially produced, in order to perform some definite -purpose in the economy;—whatever substances are separated from the -mass, and carried out of the system on account of their useless or -noxious properties:—all are derived from the nutritive fluid, the -blood, and are formed from it by the process of secretion. - -710. In this function are included the most secret and subtle processes -of the vital economy,—the ultimate actions of the organic life. Of -the real nature of those actions nothing definite is known; and -they are modified by agencies over which the art and skill of the -experimentalist can exert no adequate control. It is not wonderful -therefore that they should be involved in obscurity: nevertheless, -when all the phenomena are collected and compared, much of the -mysteriousness in which the function appears at first view to be -involved vanishes. - -711. The apparatus of secretion is infinity varied in form: when -examined in its complex combinations it appears inextricable in -structure, but the diligence and skill of modern research have unfolded -much of its mechanism, and enabled us to trace the successive steps by -which it passes from its simple to its complex condition. - -712. To form an organ of secretion there must be an artery, a vein, -a nerve, an absorbent, and a sufficient quantity of cellular tissue -to allow of the free expansion of these vessels and of their complete -intercommunication. Membrane constitutes such an organ; for membrane -is composed of arteries, veins, nerves, and absorbents sustained and -connected by cellular tissue. Hence membrane constitutes a secreting -organ, in its simplest form. The most important secreting membranes are -the serous (30), the cutaneous (34), and the mucous (33). - -713. Serous membrane which lines the great cavities of the body, and -which gives an external covering to the organs contained in them (fig. -LX. a, c), forms an extensive secreting surface. Synovial membrane, or -that which covers the internal surface of joints, and which constitutes -an important portion of the apparatus of locomotion, is essentially the -same in structure and office. - -714. Cutaneous membrane, or the skin, which forms the external covering -of the body, is an organ in which manifold secretions are constantly -elaborated; but the skin is only a modification of the membrane -which lines the interior of the body, the mucous. Mucous membrane -forms the basis of the secreting apparatus placed in the mouth, -fauces, esophagus, stomach, and intestines in their whole extent; of -the secreting apparatus auxiliary to that of the alimentary canal, -namely, the pancreas and the liver; probably also of the mesenteric, -or lacteal glands, together with the vast system of lymphatic glands, -and certainly of the glands of the larynx, trachea, bronchi and -air vesicles of the lungs. Hence, while membrane forms the basis -of the secreting apparatus in general, mucous membrane is far more -extensively employed in its construction than any other form of -membrane. - -715. 1. In the construction of the secreting apparatus, membrane -disposed in the simplest form, constitutes merely a uniform, smooth, -extended surface. Serous membrane is always disposed in this simple -mode. The costal pleura which lines the internal surface of the walls -of the chest (fig. LX. a); the pulmonary pleura which is continued from -the walls of the chest over the lungs (fig. LX. 5); the peritoneum -which lines the internal surface of the cavity of the abdomen, and -which is reflected over the viscera contained in it (fig. LX. c, and -6, 7, 8, &c.); the synovial membrane which covers all the articular -surfaces; the arachnoid membrane which envelopes the brain, form -simple continuous, serous, secreting surfaces. On the contrary, mucous -membrane is never disposed in this perfectly simple mode; even when it -forms a continuous surface, as in the lining, which it affords to the -alimentary canals, it is more or less plaited into folds or rugæ (fig. -CLXVII. 1). - -[Illustration: Fig. CLXXXI. - - A portion of the mucous surface of the intestines, showing some of the - mucous glands which present the appearance of fovæ or cryptæ.] - -716. 2. The second disposition of membrane in the construction of the -secreting apparatus, is the depression of it into a minute pit or fova, -called a crypt (CLXXXI.), which is sometimes inclosed on all sides, -forming a cell or vesicle (fig. CXXXVIII.). - - -[Illustration: Fig. CLXXXII. - - Portion of the skin and cellular tissue, showing the sebaceous - follicles, as seen under the microscope very highly magnified. 1. The - external surface of the follicles with the blood-vessels ramifying - upon it. 2. Follicles laid open, showing the interior cavity into - which the secreted fluid is poured.] - -717. 3. Next, the vesicle, instead of being rounded, is elongated into -a peduncle or neck, not unlike the neck of a bottle (fig. CLXXXII. 1). -This pedunculated vesicle is called a follicle. - -718. 4. Then, the follicle is somewhat elongated, without neck and -without terminal expansion (fig. CLXXXVI. 1); and this is called a -cæcum or pouch. - -719. 5. And, lastly, the cæcum itself is elongated; so that instead of -presenting the appearance of a pouch, it rather resembles a tube (fig. -CLXXXV. 1), and is accordingly named tubulum. - -720. In the construction of the secreting apparatus, membrane, then, -may be said to be disposed into four elementary forms constituting -cryptæ or vesicles, follicles, cæca and tubuli. Membrane, disposed -into these elementary forms, constitutes the simple bodies by the -accumulation and the varied arrangement of which the compound organs -are composed. There is no other known element which enters into the -composition of the most complex secreting organ. - -721. One of these elementary bodies may exist as a simple organ, or -many may be collected into a mass to form a compound organ. When single -they are called solitary: when collected into a mass, aggregated. Each -elementary body has a mode of aggregation peculiar to itself. Vesicles -aggregate by clustering together (fig. CXXXVIII.), and adhering as -if by a common stem (fig. CXXXVIII.); follicles by uniting at their -orifices (fig. CLXXXIII.), and forming masses which are disposed either -in a linear direction (fig. CLXXXIII.) or in fasciculi (fig. CLXXXIV.); -cæca by forming bundles, parallel or branched (fig. CLXXXVI.); -and tubuli by forming masses straight (fig. CLXXXV.), tortuous or -convoluted (figs. CLXXXV. and CLXXXIX.). - -[Illustration: Fig. CLXXXIII. - - Aggregated follicles disposed in a linear direction, here represented - of their natural size, as seen near the mouth in the goose.] - -[Illustration: Fig. CLXXXIV. - - Conglomerated follicles.] - -722. When a single elementary body, as a vesicle or follicle, forms -a distinct secreting organ, the matter secreted is elaborated at the -inner surface of the organ (fig. CLXXXII. 2), and is contained within -its cavity. When needed it quits this cavity through the walls of -the vesicle, or at the orifice of the follicle, on the application -of the appropriate stimulus. When a number of cryptæ or vesicles are -aggregated into clusters, the individual vesicles sometimes open by -distinct orifices into a common receptacle or sac (fig. CLXXXIV.). When -follicles are aggregated into a mass, and the mass is disposed in a -linear direction (fig. CLXXXIII.), each follicle pours out its secreted -matter by its own orifice (fig. CLXXXIII.); but if conglomerated, into -a common mass by a common orifice (fig. CLXXXIV.). - -[Illustration: Fig. CLXXXV. - - 1. Parallel tubuli, opening by distinct orifices into—2. A common - cavity.] - -[Illustration: Fig. CLXXXVI. - - Branched cæca, showing—1. The cæca terminating in—2. Excretory ducts - which unite to form—3. A common trunk.] - -723. In like manner, in some very simple arrangements of cæca and -tubuli, each body opens by its own distinct orifice (fig. CLXXXV. -2). But in the more complex arrangements of these bodies, it is -indispensably necessary to modify this mode of parting with their -contents. When the elementary bodies are aggregated into dense, -thick masses (fig. CLXXXIX.), when layer after layer of these masses -containing myriads of myriads of follicles, cæca, or tubuli, are -superimposed one upon another, (fig. CLXXXIX.), it is impossible that -each individual body can have a separate orifice. In this case a -minute tube springs from each body (fig. CLXXXVI. 2); and a complete -connexion is established between all the individuals composing the -mass by the free intercommunication of these tubes (fig. CLXXXVI. 2). -Of these tubes the minutest unite together, and form larger branches -(fig. CLXXXVI. 2); these larger branches again uniting form still -larger branches (fig. CLXXXVI. 2), until, by their successive union, -the branches form at length a single trunk (fig. CLXXXVI. 3), with -which all the individual branches, whether great or small, communicate, -and into which they all pour their contents (fig. CLXXXII. 2, 3). -The bodies from which these tubes take their origin, and the minute -tubes themselves, are called secreting canals (fig. CLXXXII. 1, 2); -the common trunk formed by their union is termed the excretory duct -(fig. CLXXXII. 3). The secreting canals contain the secreted matter; -the excretory duct collects this matter, and conveys it to the part of -the body in which it is appropriated to the specific purpose which it -serves in the economy. - -724. The basis of the secreting canals consists, then, of membrane -disposed in one or other of the elementary forms described (712, _et -seq._), These secreting canals constitute a peculiar system of organs -wholly different from all the other organs of the body. The form of -these organs, their structure and their relation to the blood-vessels -and nerves, have formed subjects of laborious investigation and of -keen controversy during several centuries. The honour of discovering -the exact truth on these points is due to very recent researches. - -725. Malpighi, an Italian, who flourished at Bologna in the middle of -the 17th century, was the first to establish a special inquiry into -the intimate structure of the secreting apparatus. After many years -of laborious examination he arrived at the conclusion that a minute -sac or follicle is invariably interposed between the termination of -the capillary artery and the commencement of the excretory duct. -According to him, the capillary artery conveys the blood to the -follicle, separates from the blood the substance secreted, and the -excretory duct arising from one extremity of the follicle conveys the -secreted fluid, when duly prepared, to its destined situation. By -injection, by dissection, by the microscope, by experiment on living -animals, and by the phenomena of disease, he conceived that he had -demonstrated that this is the true structure of the secreting apparatus -in its most complex form. This view was generally acquiesced in by his -contemporaries and by succeeding anatomists and physiologists; and in -the time when Ruysh wrote was the received opinion. - -726. Ruysh, who flourished at Amsterdam, and was contemporary with -Malpighi, but a younger man, and who published on the glands about -twenty years after Malpighi, according to the account of Haller, -“employed wonderful patience, with the assistance of his daughters, -in rendering all his preparations elegant and beautiful, being -equally skilled in the methods of softening, hardening, filling, and -drying.” Of Ruysh it was said that while others, in their anatomical -preparations, merely exhibited the horrid features of death, he -preserved the human body in all the freshness of life, even to the -expression of the features. The fineness of his injections, the -dexterity with which he unfolded the minute vessels, nerves, and -absorbents, and exhibited their combinations and relations in the most -delicate structures, the skill with which he preserved his preparations -in transparent fluids, and the elegance with which he displayed them -in their natural forms and folds, excited universal admiration; and -philosophers, statesmen, princes, kings, all the learned and noble of -the day, crowded to his museum. - -727. By his superior method of injecting, Ruysh conceived that he was -able completely to disprove Malpighi’s doctrine. He maintained that -the bodies which Malpighi mistook for sacs or follicles are in reality -convoluted vessels; that these vessels are capable of being completely -unravelled; that, when unfolded, their continuity with the excretory -duct is perfectly demonstrated; that secretion is performed by the -capillary artery itself, without the intervention of any other organ; -and that when the secreted substance is duly prepared, it is poured by -the capillary directly into the excretory duct. - -728. Modern research has demonstrated that the opinion of Malpighi -approaches nearer the truth than that of Ruysh, who appears to have -mistaken the secreting canals for the ultimate division of the -arterial vessels. Malpighi, indeed, did not succeed in discovering -the elementary bodies of which the secreting apparatus is composed; -but he arrived at the very verge of the truth. Profiting by the art -which Ruysh brought to so much perfection, by the facts which Malpighi -disclosed, and, above all, by the improved structure of the microscope, -and the increased skill which has been acquired in the manipulation -of the instrument, the modern physiologist is enabled to see what -was formerly beyond the cognizance of sense, and to demonstrate what -before could only be matter of conjecture. Availing himself of these -advantages with consummate skill, and applying himself to the task with -indefatigable industry, Professor Müller, of Berlin, has investigated -the structure of the secreting apparatus in the whole animal kingdom, -and has traced the progressive development of the several secreting -organs through the entire animal series, from their simplest form in -the lowest animal, to their most complex in the highest. - -729. From the researches of this physiologist, and from the labours of -others, his countrymen and contemporaries, who have engaged in the -investigation with an ardour second only to his own, it is demonstrated -that the secreting apparatus of the animal body is disposed in one -or other of the elementary forms which have been described. The -blood-vessels are distributed upon the walls of these elementary -bodies, whether simple cryptæ follicles, cæca, or tubuli, or whether -these bodies are accumulated and combined into the largest and most -complex series of secreting canals, just as the branches of the -pulmonary artery are distributed upon the walls of the air-vesicles -in the rete mirabile of the lungs. The air-vesicles of the lungs are -secreting organs, and afford an excellent example of the mode in which -the blood-vessels are distributed upon the walls of the elementary -secreting bodies. The arteries do not form continuous tubes with the -secreting bodies or their excretory ducts, as was maintained by Ruysh; -neither is the secreting body interposed between the termination of -the artery and the commencement of the excretory duct, as was thought -by Malpighi; but the ultimate divisions of the arteries are spread -out upon the walls of the secreting bodies, where they terminate in -veins by a delicate vascular net-work (fig. CLXXXVII. 2). The minutest -branch of the artery is always smaller than the minutest secreting -body on the walls of which it is distributed. According to Müller, the -arteries, spread out upon the walls of the secreting bodies, form a -distinct and peculiar system of vessels visible under the microscope. -In the more complex secreting organs, immediately before reaching their -distribution upon the walls of the secreting canals, the ultimate -divisions of the arteries form an intricate and delicate net-work -(fig. CLXXXVII. 2). When at length they reach the secreting canals the -arteries no longer divide and subdivide, but are always of the same -uniform size in the same secreting organ, though their magnitude is -different in every different kind of secreting organ. These ultimate -divisions of the arteries are the proper capillary arteries. It is in -these arteries that the changes are wrought upon the blood which it -is the object of the various processes of secretion to effect. In the -walls of these arteries there are visible no pores, no apertures, no -open extremities by which the secreted fluid, when formed from the -blood, is conveyed into the cavity of the secreting canals; it probably -passes through the walls of the vessels into the secreting canals by -the process of endosmose (804). - -[Illustration: Fig. CLXXXVII. - - A thin portion of the surface of the kidney taken from the scianus, - showing—1. The termination of the cæca forming the uriniferous - duct; and—2. A delicate vascular net-work, consisting of capillary - blood-vessels about to be distributed on the walls of the cæca.] - -730. Secreting organs are very abundantly supplied with nerves, -which are derived for the most part from the organic portion of the -nervous system; although for the reasons assigned (vol. i. p. 77, _et -seq._) sentient nerves are mixed with the organic. The more important -secreting organs have each a distinct net-work or plexus of organic -nerves, which surround the blood-vessels distributed to the organ, -(fig. CLXX. 3), and which envelopes more especially the arterial trunks -and their larger branches (fig. CLXX. 3). From these plexuses nervous -filaments spring in countless numbers (fig. CLXX. 3), which are spread -out upon the walls of the arteries, just as the arteries are spread -out upon the walls of the secreting canals. The nerves never quit -the arteries; are never spent upon the membranous matter which forms -the basis of the secreting organ, but are lost upon the walls of the -capillary arteries. The nerves uniformly increase in number and size as -the arteries diminish in magnitude and as their capillary terminations -become thinner and thinner. - -731. When the secreting apparatus consists of simply extended membrane, -a close net-work of capillary arteries with their accompanying nerves -is spread out over the whole extent of the secreting surface. This -simple arrangement is sufficient to separate from the blood the simple -secretion in this case required. - -732. When the secreting apparatus consists of simple cryptæ, follicles, -cæca, or tubuli, a similar net-work of capillary arteries and nerves -is spread out on the sides of this more extended surface. The more -elaborate secretion now formed is received into the interior of these -organs, where it remains for some time, and whence it is ultimately -conveyed as it is needed by the actions of the system. - -733. But when the secreting apparatus consists of aggregates of cryptæ, -follicles, cæca, and tubuli, with their net-works of arteries and -nerves, a much more complex structure is built up, which is destined to -perform a proportionably elaborate function. An aggregation of these -secreting bodies into a large mass, enveloped in a common membrane, -so as to form a distinct body of a solid consistence, constitutes the -organ termed a gland. Simply extended membrane, with its apparatus -of arteries and nerves does not constitute a gland. Simple cryptæ, -follicles, cæca, and tubuli, with their larger apparatus of arteries -and nerves, do not constitute a gland. The first is simply secreting -surface; the second are simply secreting cryptæ, follicles, cæca or -tubuli; but when these bodies are aggregated into dense and solid -masses with an extended system of excretory ducts, and when the whole -of this apparatus is inclosed in a proper membrane so as to form a -distinct body, such a body is termed a gland. - -734. Primary aggregations of these secreting bodies constitute what is -termed a conglobate, that is, a simple gland; such are all the glands -connected with the absorbent or lymphatic system. Secondary aggregates, -or aggregates composed of simple glands, constitute what is termed -a conglomerate, that is, a compound gland; such are all the organs -commonly termed viscera, as the liver, the spleen, the pancreas, the -kidney, and so on. - -735. The conglobate, or simple gland, being formed by the aggregation -of cryptæ, follicles, cæca, or tubuli, inclosed in a proper membrane, -presents the appearance of a simple solid body, commonly of a rounded -or oblong form (fig. CLXXVI. 516). On the contrary, the conglomerate -or compound gland, being formed by the aggregation of conglobate or -simple glands, presents the appearance of a compound body composed of -a congeries of masses (fig. CLXV. 1). The larger masses enveloped in -their own proper membrane are termed lobes (fig. CXCI.); the smaller -masses, also enveloped in their own proper membrane, are termed lobules -(fig. CXCI.); the lobules, when carefully examined, are seen to be -composed of still smaller masses, and these of masses yet more minute, -until at length patient, laborious, and skilful dissection brings into -view the ultimate constituent elements, which are invariably found to -consist of simple cryptæ, follicles, cæca, or tubuli. - -736. Thus membrane having a specific arrangement of blood-vessels and -nerves, from being simply extended, is folded into a few elementary -forms; the bodies which result constitute simple secreting organs; -these bodies collected together form, by their aggregation, compound -organs; the compound organs, uniting, form aggregates still more -compound, until at length a structure is built up highly elaborate and -complex. But this complexity of combination and arrangement does not -alter the constitution of the organs; their form varies, but their -nature remains essentially the same. All consist alike of membrane -organized in a similar mode. The complex contains no element not -possessed by the simple gland, and the gland contains no element not -possessed by the secreting surface. But there is this difference in -the complex organs. Every kind and degree of change in the form of the -secreting apparatus, from membrane simply extended, to membrane coiled -up into the most complex gland, is attended with an accumulation and -concentration of secreting surface. The crypt contains a larger extent -of secreting surface than the simple membrane; the follicle than the -crypt; the cæcum than the follicle; and the tubulum than the cæcum. A -certain amount of secreting surface is gained by the disposition of the -simple membrane into the form of the crypt. The collection of a number -of crypts into a cluster doubles the extent of the secreting surface by -the extent of every crypt that is added to the cluster. The addition -of every cluster doubles the whole extent of surface acquired by a -single cluster. But when stems spring as if from a common trunk; when -branches spring from a stem; when small branches spring from the large -branches, and yet smaller branches from the small in a series, which -the eye, assisted by the most powerful microscope, is wholly unable to -trace; when all the clusters thus formed are collected, and combined -into a compact mass, the intricacy of which no art can completely -unravel, the extent of surface obtained is altogether immeasurable. How -immense must be the extent of surface thus acquired in such an organ as -the human lungs, in such a gland as the human liver! - -737. In such an aggregation the concentration is also equal to the -accumulation; the maximum of surface is comprised in the minimum of -space, and the energy and elaborateness of the function of a secreting -organ is uniformly proportionate to such a concentration of its -secreting substance. - -[Illustration: Fig. CLXXXVIII. - - Aggregated and clustered cæca opening into the alimentary canal, - performing the function of the liver.] - -738. Hence the complexity of the compound gland in the higher animals -would appear to arise solely from the intricate arrangement of the -immense mass of secreting matter concentrated in a small compass; -hence also the progressively increased complication indicated in the -successive development of the glandular system in the animal series. -Thus, for example, among the distinct organs formed for the purpose -of elaborating a specific secretion, being intimately connected with -the process of digestion, one of the first is the salivary gland. Low -down in the scale, in the animal in which the first rudiment of a -salivary gland is traceable, it consists of a single follicle, which -appears to serve the office of a gland. In an animal a little higher -in structure, two, three, or four follicles combine to form a somewhat -less simple organ. In an animal still higher in the series, a number of -follicles are clustered together and form a much more complex organ; -and in this manner, as the organization of the animal becomes higher -and higher, the complexity of the gland increases, until at length it -is composed of a countless number of follicles collected into clusters, -the clusters disposed into lobes, the lobes subdivided into lobules, -and the lobules into still smaller particles, the ultimate elements -of the glandular apparatus. In like manner, when the first rudiment -of the liver is discoverable, it consists of a single pouch or cæcum; -somewhat higher in the series, the organ is composed of two or more -cæca distinct and free; and then, as its complexity increases with -the perfection of the organization, cæca are accumulated upon cæca; -the aggregates so formed are closely compacted, disposed into lobes, -divided into lobules, and subdivided into the ultimate particles of the -glandular apparatus. So in a gland composed of tubuli, as the kidney, -the organ in its rudimentary state consists of a few straight tubuli: -as its structure advances more tubuli are added: next, the increasing -tubuli superimposed one upon another become tortuous; then the tubuli -still accumulating, become not merely tortuous, but convoluted; and -last of all, countless numbers of tubuli are closely compacted into -exceedingly convoluted masses. Uniformly, the lower the animal and the -simpler the organ, the larger and the more manifest are the elementary -parts of the gland; but in the higher animals these elementary bodies -are so minute as to be altogether microscopical and their arrangement -is so complex that it can be unravelled only with extreme difficulty. - -[Illustration: Fig. CLXXXIX. - - Portions of the kidney taken from the ophidian reptile, as seen - under the microscope, highly magnified. A one portion of the kidney, - showing—1. The trunk of the artery passing to be distributed to—2. The - diverging tubuli, forming the uriniferous ducts which terminate in—3. - The common excretory duct called ureter.—B another portion of the same - kidney, showing the extremely convoluted course of—4. The uriniferous - ducts. 5. The smaller excretory ducts, or secreting canals, converging - and uniting to form—6. The common excretory duct called the ureter.] - -739. It is a striking confirmation of the correctness of this view -of the structure of the glandular apparatus, that whenever in the -ascending series a gland appears for the first time in any class, the -elementary bodies are so large, and are disposed in so simple a mode, -that a slight examination is sufficient to demonstrate their primitive -form, and to render it manifest that they consist either of vesicles, -follicles, cæca, or tubuli, more or less aggregated. This is seen -in the obvious structure presented by the liver, the pancreas, the -salivary glands, and the mammæ, in the simple animals in which these -organs first appear. Thus the liver in animals low down in the scale -is manifestly composed of simple clustering follicles: in the fish the -pancreas is composed of simple branched follicles: in the bird, the -salivary glands are composed of simple parallel tubuli; and in the -cetacea the breasts are composed of simple branched tubuli. - -[Illustration: Fig. CXC. - - A lobule of a gland in the progress of development in the ovum of - the bird, as seen under the microscope, showing the origin of the - excretory ducts in the semipellucid gelatinous blastema, and the - branching and foliated arrangement of the follicles in which the - excretory ducts terminate.] - -740. But the microscope, by bringing the successive development of the -compound gland in the embryo of the higher animal under the cognizance -of sense, perfectly discloses the nature of its composition. In -the development of the incubated egg every step of the progressive -formation of the compound gland is rendered visible to the eye. -When this process is carefully watched, it is seen that the part of -the gland first formed is the excretory duct, which springs from -the blastema, the common mass of matter out of which all the organs -are formed. From this duct the elementary parts of the gland bud -just as bunches of grapes bud from the stalk. The buds, at first -at considerable distances from each other, approach nearer as they -increase by new growths, until at length they come into actual -contact. The growth continuing, and the compactness of the substance -of the gland proportionally increasing, the primitive form of the -elementary bodies which compose it is ultimately lost. The substance -of the gland now appears to consist of compact solid matter, which -is commonly termed parenchyma. The component particles of this -parenchymatous and apparently solid substance present a clustered or -grape-like appearance, from which they early obtained the name of -acini, from the Latin word acinus, a berry. This term, originally -employed merely to express the clustered and branching appearance -of the elementary parts of the gland, has since been used in widely -different senses. By some it has been employed to express solid -glandular grains constituting a supposed distinct parenchymatous -substance, differing in every different gland. It is now proved that no -such solid granular particles enter into the composition of any gland -in the animal kingdom. By others the term acini has been employed to -express granular bodies composed of blood-vessels, directly continuous -with the excretory ducts, and from which the excretory ducts derive -their origin. Recent investigation has demonstrated that there is no -continuity of the blood-vessels into the excretory duct either in the -acini or in any other part of the gland. It is established that the -blood-vessels are spread out upon the walls of the secreting canals -and do not form with them continuous tubes. The bodies which have been -mistaken for granular particles, constituting the so called solid -acini, are really the shut extremities of hollow follicles, cæca, or -tubuli, which appear solid only from the closeness with which they are -compacted. When carefully dissected and examined under the microscope, -their real nature becomes apparent, and this is also sometimes capable -of being demonstrated by injection; for some of these elementary bodies -are vesicular, and can be filled with mercury, when they present a -beautiful appearance like clusters of diamonds; or they may be inflated -with air, just as the air vesicles of the lungs. - -[Illustration: Fig. CXCI. - - Section of the liver in the lower animal in the progress of - development, as seen under the microscope, showing the rudimentary - division into lobes and lobules, and the elongated terminations of - the biliferous ducts, or cylindrical acini variously disposed in a - branching and foliated manner.] - - -741. On watching the formation of the gland in the development of -the embryo, it would appear that at first free streams of blood, or -blood not contained in proper vessels, pass around the acini, the shut -extremities of the excretory ducts, or the secreting canals. “So it -would seem,” says Müller, “when we examine the evolution of the liver -and kidney in the embryo of the lower animal; for the interstices of -the canals appear bloody, without the slightest trace of the walls of -blood-vessels. I conceive that in the beginning new streams arise in an -amorphous mass (a mass without form), not bounded by proper parieties; -but that soon walls are formed, which present definite boundaries -to the streams, the density of the substance around the streams -gradually increasing.” It is in this manner that the connexion is first -established between the system of capillary blood-vessels and that of -the secreting organs. - -742. In its embryo state the compound gland of the highest animal -consists of mere excretory ducts, wonderfully similar to the simple -secreting bodies of the lowest classes. But in the higher animal this -simple form of the gland is transient: gradually, with the progressive -evolution of the embryo, it passes into a more complex structure; while -in the lower animal the simple form of the gland remains permanently -the same through the whole term of life. - -743. Such are the main points which have been ascertained relative to -the structure of the secreting apparatus, which enters in one or other -of its forms, as a constituent element, into almost every part of -the animal body. Wherever there is nutrition there is secretion, and -wherever there is secretion there is one or other of these secreting -bodies. How immense the number of these organs in the human body! Every -point in the interior of the walls that bound the great cavities is a -secreting surface. Every point of the secreting surface that lines the -alimentary canal, from its commencement to its termination, is studded -with distinct secreting organs. Every point of the skin is still more -thickly studded with distinct secreting organs. By the naked eye, and -still more distinctly with a lens, may be seen the pores through which -the vapour that constitutes the insensible perspiration incessantly -exudes. Next are the open mouths of myriads of sebacious follicles that -pour out upon the skin the oily matter which gives it its suppleness -and softness; and besides all these, are the hairs, each the product -of a secreting organ placed immediately beneath the skin. An attempt -to count the number of pores and hairs visible to the eye within the -compass of an inch, and thence to compute the number on the whole -surface of the skin, may convey some conception of the amount of these -organs; yet these form but a small part of the secreting apparatus. -The great viscera of the body, the brain, the lungs, the liver, the -pancreas, the spleen, are portions of it; all the organs of the senses, -the eyes, the ears, the nose, the tongue; all the organs of locomotion; -every point of the surface of every muscle, and a great part of the -surface and substance of the very bones are crowded with secreting -organs. - -744. Since every secreting organ is copiously supplied with blood, -it follows that a great part of the blood of the body is always -circulating in secreting organs; and, indeed, it is to afford materials -for the action of these organs that the blood itself is formed. - -745. How do these organs act upon the blood? All that is known of the -course of that portion of the blood which flows through an organ of -secretion is, that it passes into arteries of extreme minuteness, which -are spread out upon the external walls of the elementary secreting -bodies, and which, as far as they can be traced, pass into capillary -veins,—nowhere terminating by open mouths—nowhere presenting visible -outlets or pores; their contents probably transuding through their thin -and tender coats by the process of endosmose. - -746. As it is flowing through these capillary arteries, the blood -undergoes the transformations effected by secretion, forming—1. The -fluids, which are added to the aliment, and which accomplish its -solution, and change it into chyme. 2. The fluids, which are added to -the chyme to convert it into chyle, and both to chyle and lymph, to -assist in their assimilation. 3. The fluids which, poured into the -cavities, facilitate automatic or voluntary movements. 4. The fluids, -which serve as the media to the organs of the senses by which external -objects are conveyed to the sentient extremities of the nerves for -their excitement. 5. The fluids which, deposited at different points -of the cellular tissue, when more aliment is received than is needed, -serve as reservoirs of nutriment to be absorbed when more aliment is -required than can be afforded by the digestive organs. 6. The fluids -which are subsequently to be converted into solids. 7. The fluids which -are eliminated from the common mass, whether of fluids or solids, to be -carried out of the system as excrementitious substances. 8. In addition -to all these substances, which are indispensable to the preservation of -the individual, those which are necessary to the perpetuation of the -species. - -747. In order to form any conception of the mode in which the secreting -organs act upon the blood, so as to elaborate from it such diversified -substances, it is necessary to consider the chemical composition of the -different products of secretion, and the degrees in which they really -differ from each other, and form the common mass of blood out of which -they are eliminated. - -748. By chemical analysis, it is established that all the substances -which are formed from the blood by the process of secretion are either -water, albumen, mucus, jelly, fibrin, oil, resin, or salts; and, -consequently, that all the secretions are either aqueous, albuminous, -mucous, gelatinous, fibrinous, resinous, oleaginous, or saline. - -749. 1. AQUEOUS SECRETIONS.—From the entire surface of the skin, and -also from that of the lungs, there is constantly poured a quantity of -water, derived from the blood, mixed with some animal matters, which, -however, are so minute in quantity, that they do not communicate to the -aqueous fluid any specific character. - -750. 2. ALBUMINOUS SECRETIONS.—All the close cavities, as the thorax, -the abdomen, the pericardium, the ventricles of the brain, and even -the interstices of the cellular tissue, are constantly moistened by a -fluid which is termed serous, because it is derived from the serum of -the blood. This serous fluid consists of albumen in a fluid form, and -it differs from the serum of the blood chiefly in containing in equal -volumes a smaller proportion of albumen. Membranes of all kinds consist -essentially of coagulated albumen; and the albumen, as constituting -these tissues, differs from albumen as existing in the serum of the -blood only in being unmixed with extraneous matter, and in being in a -solid form. - -751. 3. MUCOUS SECRETIONS.—As all the close cavities, or those which -are protected from the external air, are moistened with a serous -fluid, so all the surfaces which are exposed to the external air, as -the mouth, the nostrils, the air-passages, and the whole extent of the -alimentary canal, are moistened with a mucous fluid. Mucus does not -exist already formed in the blood. It is always the product of a gland. -Some of the mucous glands are among the most elaborate of the body; -still the main action of the gland seems to be to coagulate the albumen -of the blood, for the basis of mucous is coagulated albumen. The fluid -that lubricates the mucous surfaces in their whole extent, the saliva, -the gastric juice, the tears, the essential part of the fluid formed -in the testes and in the ovaria, are mucous secretions. Hence the most -complex and elaborate functions of the body, respiration, digestion, -reproduction, are intimately connected with the mucous secretions: -nevertheless, as far as regards their chemical nature, the mucous -differ but slightly from the albuminous secretions; and it is probable -that a slight change in the secreting organ is sufficient to convert -the one into the other. By the irritation of mercury on the salivary -glands, the saliva, properly of a mucous, is sometimes converted into a -substance of an albuminous nature; and irritation in some of the serous -membranes occasionally causes them to secrete a mucous fluid. - -752. 4. GELATINOUS SECRETIONS.—The proximate principle termed jelly -abounds plentifully in several of the solids of the body, and more -especially in the skin; but jelly does not exist already formed in -the blood. Yet it is not the product of a gland, neither is there any -known organ by which it is formed. Out of the body albumen is capable -of being converted into jelly by digestion in dilute nitric acid: this -conversion is probably effected by the addition of a portion of oxygen -to the albumen. Albumen contains more carbon and less oxygen than -jelly; the proportions of hydrogen and nitrogen in both being nearly -the same. According to MM. Gay Lussac and Thénard, the elements of -albumen and jelly are, - - Carbon. Oxygen. Hydrogen. Nitrogen. - - Albumen 52.883 23.872 7.54 15.765 - Jelly 47.881 27.207 7.914 16.988 - -The conversion of albumen into jelly is incessantly going on in the -system; and the process accomplishes most extended and important uses. -In the lungs at the moment of inspiration oxygen enters into the blood -in a state of loose combination; but in the system, at every point -where the conversion of albumen into jelly takes place, oxygen probably -enters into a state of chemical combination with albumen; and the new -proximate principle, jelly, is the result. The agent by which this -conversion is effected appears to be the capillary artery: the primary -object of the action is the production of a material necessary for -the formation of the tissues of which jelly constitutes the basis, as -the skin; but a secondary and most important object is the production -of animal heat; the carbon that furnishes one material of the fire -being given off by the albumen at the moment of its transition into -jelly; and the oxygen that furnishes the other material of the fire -being afforded to the blood at the moment of inspiration. This view -affords a beautiful exposition of the reason why jelly forms so large a -constituent of the skin in all animals. The great combustion of oxygen -and carbon, the main fire that supports the temperature of the body, is -placed where it is most needed, at the external surface. - -753. 5. FIBRINOUS SECRETIONS.—The pure muscular fibre, or the basis -of the flesh, is identical with the fibrin of the blood. It contains -a larger proportion of nitrogen, the peculiar animal principle, and -is consequently more highly animalized than the preceding substances. -It appears to be simply discharged from the circulating blood by the -capillary arteries, and deposited in its appropriate situation; no -material change in its constitution being, it would seem, necessary to -fit it for its office. - -754. 6. OLEAGENOUS SECRETIONS.—Fat of all kinds, which is found so -extensively connected with the muscles, and with many of the viscera, -and which is more or less diffused through the whole extent of the -cellular tissue, marrow, milk, and nervous and cerebral matter, are -essentially of the same nature. The basis of them all is oil; and oil -exists already formed both in the chyle and in the blood. - -755. 7. RESINOUS SECRETIONS.—The peculiar substance forming the basis -of bile, picromel; the peculiar substance forming the basis of urine, -urea; the peculiar substance connected with the muscular fibre, and -forming a component part of almost all the solids and fluids of the -body, osmazome, consists of a common principle—a resin, which exists -already formed in the blood, and more especially in the serosity of the -blood. - -756. 8. SALINE SECRETIONS.—The substances termed saline, namely, the -acids, the alkalis, and the neutral and earthy salts, are disposed -over every part of the system: they enter more or less into all the -constituents both of the solids and fluids; they form more especially -the phosphate of lime, the earthy matter of which bones are composed; -and they all exist already formed in the blood. - -757. From this account, then, it appears, that by chemical analysis, -the blood is ascertained to contain water, albumen, fibrin, oil, resin, -and various saline and earthy substances: it follows, that, with the -exception of the absence of jelly, the constituents of the body and the -constituents of the blood are nearly identical; and it is probable that -they will be found to be perfectly identical when their analysis shall -have become complete. - -758. It is also manifest that in by far the greater number of cases the -various substances of which the body is composed are simply separated -from the nutritive fluid at the parts of the body at which they are -deposited; and that, existing already formed in the blood, they are -merely deposited there, and not generated. Still, however, since it is -certain that gelatin cannot be recognized in the blood, and since it -is doubtful whether some other substances found in different textures -and secretions really exist in the blood, it is necessary, in the -present state of our knowledge, to suppose, that although most of the -constituents of the living tissues are contained in the blood, yet that -in some instances a material change is effected in their nature at -the time and place of their escape from the circulation; and that in -these cases the secreted substances are not simple extracts from, but -products of, the blood. - -759. It is by the apparatus of secretion that this separation, -evolution, or re-formation, is effected. Out of a fluid which contains, -blended together, almost all the heterogeneous substances of which the -body is built up, particular substances are selected from the common -mass, and are deposited in certain parts, and only in certain parts. -Although by the most careful examination of the structure of the -apparatus, it is not possible to form a precise conception of the mode -in which this separation is effected, yet we are enabled to perceive a -number of contrivances which we can readily understand must conduce to -the accomplishment of the object. - -760. 1. Of these, the most obvious is mechanical arrangement. - -761. In its passage to different organs the blood is propelled -through canals of extreme minuteness: in every different case these -canals differ from each other in size; pass off from their respective -trunks at different angles; possess different degrees of density; are -variously contorted, and are of various lengths. In some they are -straight, in others convoluted; at one time branching, at another -pencillated, and at another starry. The veins, too, in some cases, are -almost straight, in others exceedingly tortuous, in others reticulated; -and the freedom of their communication with the arteries varies so -much, that in some cases fine injections pass from the one set of -vessels to the other with the greatest facility, while, in others -they pass with extreme difficulty. The consequence of these divers -arrangements of the capillary blood-vessels is, that the current of -the blood must necessarily flow in them with different degrees of -velocity; its particles must be placed at different distances from each -other, and must be presented to each other in different positions and -in widely different proportions. In no two secreting organs are any -two of these conditions exactly alike. In the lower orders of animals, -in which secretion is seen in its simplest condition, the general -nutritive fluid, elaborated and contained in a single internal cavity, -appears to furnish a variety of products very different from itself, by -a process hardly more complex than mere transudation through a living -membrane. In the higher animals the different secreting organs may be -considered, in part at least, as mechanical contrivances adapted to -carry on analogous transudations—fine sieves or strainers diversly -constructed. A fluid containing such heterogeneous matters as the -blood, held in combination by so slight an affinity, slowly transuding -through series of tubes, the mechanical arrangement of which is so -varied, must yield a different substance in every different case. -Thus by simply filtering the blood a vast variety of products may be -obtained, merely in consequence of a varied disposition of the minute -tubes of which the filters are composed. - -762. 2. But in the second place, this diversity of mechanical -arrangement is calculated in a high degree to promote and to modify -chemical action. The contact or proximity of the particles of bodies, -the extent of surface which those particles present to each other, the -space of time in which they continue in contact, the degree of force -with which they impinge against each other, the degree of temperature -to which they are exposed,—these, and circumstances such as these, -are conditions which exert the most powerful influence over chemical -decomposition and re-combination. In the different secreting organs, -as has been shown, the blood must necessarily pass through vessels -having every conceivable diversity of diameter: in those vessels it -must consequently flow with corresponding differences of velocity. Some -of these diameters will admit one constituent of the blood, as one of -the red particles; others may be large enough to admit two or more of -the red particles abreast; others may be so small as to be incapable of -admitting a single red particle, receiving only the more fluid portions -of the blood; in some vessels these different constituents will be in -one degree of proximity, in others in another; in some they will remain -long in contact, in others only for an instant: it is obvious that -from such different conditions the chemical products may be infinitely -varied. - -763. Such is the composition of chemical bodies, that a great diversity -of substances is obtainable merely by changing one condition, the -proportions in which the elementary particles combine. - -764. Oxygen and nitrogen combined in one proportion form atmospheric -air; in another proportion, nitrous oxide; in another, nitric oxide; -in a fourth, nitrous acid; and in a fifth, nitric acid. Few secretions -formed from the blood differ more widely from each other than the -products thus formed from these two elementary bodies. - -765. Urea consists of two prime equivalents of hydrogen, one of -carbon, one of oxygen, and one of nitrogen. Remove one of the atoms -of hydrogen, and take away the atom of nitrogen, urea is converted -into sugar; combine with urea an additional atom of carbon, it is -changed into lithic acid. In like manner add a small quantity of water -to farina, it is converted into sugar; to fibrin, it is changed into -adipocere. From a reservoir containing a quantity of substances in -the state of vinous fermentation, draw off portions of the liquor at -different stages of the process, and cause these to pass through tubes -of various diameters and with various degrees of velocity, there will -be obtained at one time an unfermented syrup, at another, a fermenting -fluid, at another, wine, at another, vinegar. Out of the body place the -blood in a state of rest, it will spontaneously separate into serum and -crassamentum, and the crassamentum will further separate into fibrin -and red particles. Add to the serum a certain portion of acid, it will -be coagulated into solid albumen; add to this solid albumen another -portion of acid, it will be converted into jelly. Add a certain portion -of acid to fibrin, it will be changed into adipose matter; bring the -acid into contact with the red particles, they will be converted into a -substance closely resembling bile. If by the rough chemistry which the -art of man can conduct so great a variety of substances may be obtained -out of a single compound, is it not wonderful that a far greater -variety should be produced by the delicate and subtle chemistry of life. - -766. 3. But a third most important agent in the process of secretion is -some influence derived from the nervous system. - -1. It is proved, by direct experiment, that the destruction of the -nervous apparatus, or of any considerable portion of it, stops the -process of secretion. By experiments performed by Mr. Brodie, it is -ascertained that the secretion of the urine is suspended by the removal -or destruction of the brain, though the circulation be maintained in -its full vigour by artificial respiration. - -2. The section, and still more the removal, of a portion of the -sentient nerves of the stomach (the par vagum, or eighth pair), -according to some experimentalists, deranges and impedes; according to -others, totally arrests the process of digestion. - -3. Other classes of phenomena illustrate in a striking manner the -influence of the nervous system over the process of secretion. -The sight, nay, even the thought of agreeable food, increases the -secretions of the mouth. Pleasurable ideas excite, painful ideas -destroy, the appetite for food; probably, in the one case, by -increasing, and, in the other, by suspending the secretion of the -gastric juice: the emotion of grief instantly causes a flow of tears; -that of fear, of urine; the sight or thought of her child fills the -maternal breasts with milk, while the removal of the child from the -mother diminishes and ultimately stops the secretion. - -767. Even the imagination is capable of exerting a powerful influence -over the process. A female who had a great aversion to calomel was -taking that medicine in very small doses for some disease under which -she was labouring. Some one told her that she was taking mercury: -immediately she began to complain of soreness in the mouth; salivated -profusely, and even put on the expression of countenance peculiar to a -salivating person. On being persuaded that she had been misinformed, -the discharge instantly began to diminish, and ceased altogether -in a single night. Two days afterwards she was again told, on good -authority, that calomel was contained in her medicines, upon which -the salivation immediately began again, and was profuse. That this -salivation was not produced by the calomel, but was the effect solely -of the influence of imagination on the salivary glands, was proved -by the absence of redness of the gums, which always takes place in -mercurial salivation, and also by the absence of the peculiar fætor, -which is characteristic of the action of this metal on the system. - -768. The same influence is apparent even in the lower animals: exhibit -food to a hungry dog, the saliva will pour from its mouth. Rob the nest -of the bird of its eggs as soon as they are laid, the bird may be made -to deposit eggs almost without end, though if the eggs are allowed to -remain undisturbed, it will lay only a certain number. The bird is led -by instinct to continue to deposit eggs in the nest until a certain -number is accumulated; that is, a mental operation acts upon the -ovarium, the secreting organ in which the eggs are formed, maintaining -it in a state of active secretion for an indefinite period; whereas -without that mental operation the secretion would be limited to a -definite number. - -769. In all these cases it is probable that the vital agent by which -the effect is produced on the secreting organs is the organic nerve. -Though the sentient part of the nervous system may in many cases be -the part primarily acted on, yet there is reason to believe that -the ultimate effect is invariably produced on the organic part, the -sentient nerves in this case acting on the organic, as in other cases -the organic act on the sentient, in consequence of that intimate -connexion which, for the reason assigned (vol. i. p. 79), is -established between both parts of this system. For, - -770. 1. The true object of the sentient part of the nervous system is -to establish a relation between the body and the external world; the -object of the organic part is to preside over the functions by which -the body is sustained and nourished, that is, over the processes of -secretion. - -771. 2. The nerves which are distributed to the secreting arteries, and -which increase in number and size as the arteries become capillary, -are, for the most part, derived from the organic portion of the nervous -system (fig. CLXX. 3). This anatomical arrangement clearly points to -some physiological purpose, and indicates the closeness of the relation -between the function of the organic nerve and the ultimate action of -the capillary artery. - -772. 3. It is demonstrated that the sentient part of the nervous -system, though occasionally influencing and modifying secretion, is not -indispensable to it. In tracing the normal or regular development of -the human fœtus, it is found that the heart is constructed and is in -full action before the brain and spinal cord, the central masses of the -sentient part of the nervous system, are in existence; and that these -masses are themselves built up by processes to which the action of the -heart is indispensable; consequently, innumerable acts of secretion -must have taken place, those, for example, which have been necessary -to form the different substances which enter into the composition of -the heart, before the brain and spinal cord exist. In like manner in -the anormal or irregular development of the fœtus, as in the production -of monsters, there may be not a vestige of head, neck, brain or spinal -cord, while there may be a perfect heart, perfect lungs, perfect -intestines, and various portions even of the osseous system. - -773. However in the perfect animal secretion may be under the influence -of the brain and spinal cord, it is clear that, since the process can -go on without them, it must be independent of them. It is a false -induction from these facts drawn by some physiologists that secretion -is independent of the nervous system. They do prove that it is -independent of one part of the nervous system, the sentient; but it -does not follow that it is independent of the other part, the organic. - -774. 4. It is demonstrated that the organic part of the nervous -system is not only independent of the sentient part, but that it -is even pre-existent to it. Researches into the development of the -nervous system, as shown in the progressive growth of the fœtus of -different animals, have proved that the existence of the organic -nerves is manifest long before that of the sentient; that nerves are -discoverable in the tissues, before the brain and the spinal cord are -formed; that as these masses become visible and grow, nerves springing -from the tissues advance towards the central nervous masses, and -at length unite with them; but that this union does not take place -until the development of the nervous system is considerably advanced. -These curious and most instructive facts show that in the fœtus, -though the brain and spinal cord may have been destroyed or have -been non-existent, yet that the organic nerves may have been in full -action. After a communication has been once established between the two -parts of the system, indeed, the destruction of the brain or spinal -cord may stop secretion, not because these organs are indispensable -to secretion; but because the destruction of one part of the system -involves the death of the other, just as the organic life itself -perishes soon after the destruction of the animal. - -775. The existence of the organic nerve is probably simultaneous -with that of the secreting artery: from the first to the last moment -of life the nerve regulates the artery; the influence of the one is -indispensable to the operation of the other; and, by their conjoint -action, the sentient nerve itself, as well as every other organ, is -constructed. - -776. There is reason to believe that the physical agent by which the -organic nerve influences secretion is electricity. The nerve appears to -be the medium by which electrical fluid is conveyed to the secreting -organs, and the nerve probably influences secretion by influencing -chemical combination, through the intervention of this most powerful -chemical agent. This is rendered probable by the observation of various -phenomena, and by the result of direct experiment. - -777. 1. It is proved that galvanic phenomena may be excited by -the contact of the nerve and muscle in an animal recently dead. A -galvanic pile may be constructed of alternate layers of nervous and -muscular substance, or of nervous substance and other animal tissues. -A secreting organ liberally supplied with organic nerve is probably -then in its physical structure nothing but a galvanic apparatus. It -is certain that some animals, as the raia torpedo, possess a special -electrical apparatus composed essentially of nervous matter; that -the nerves which compose this apparatus correspond strictly with the -organic nerves of the human body; that they are distributed principally -to the organs of digestion and secretion, and that they exert a -powerful influence over these processes; for, when the animal is -frequently excited to give shocks, digestion appears to be completely -arrested; so that, after the animal’s death, food swallowed some time -previously is found wholly unchanged. - -778. 2. It is universally admitted that the nerves in all animals -possess an extreme sensibility to the stimulus of electricity, and more -especially to that form of it which is termed galvanism. - -779. 3. Direct experiment proves that the stimulus of galvanism may -be made to produce in the living-body precisely the same effect as -the nervous influence. It has been stated, that the division of the -par vagum, in the neck of a living animal, suspends the digestion of -the food probably by stopping indirectly the secretion of the gastric -juice. If after the division of the nerves, their lower ends, that -is, that portion of the nerves which is still in communication with -the stomach, but no longer in communication with the brain, be made -to conduct galvanic fluid to the stomach, secretion goes on as fast -as when the nerves are entire and conduct nervous influence. Dr. -Wilson Philip having divided the par vagum in the neck of a living -animal, coated a portion of the lower end of the nerves with tin foil, -placed a silver plate over the stomach of the animal, and connected -respectively the tin and silver with the opposite extremities of a -galvanic apparatus. The result was that the animal remained entirely -free from the distressing symptoms which had always before attended the -division of the nerves, and that the process of digestion, which had -been invariably suspended by this operation, now went on just as in the -natural state of the stomach. On examining the stomach after death, the -food was found perfectly digested, and afforded a striking contrast to -the state of the food contained in the stomach of a similar animal, in -whom the nerves had been divided, but which had not been subjected to -the galvanic influence. - -780. 4. On applying a low galvanic power to a saline solution contained -in an organic membrane, Dr. Wollaston found that the galvanic fluid -decomposed the saline solution, and that the component parts of the -solution transuded through the membrane; each constituent being -separately attracted to the corresponding wire of the interrupted -circuit. This experiment, says this acute and philosophical -physiologist, illustrates in a very striking manner the agency of -galvanism on the animal fluids. Thus the quality of the secreted fluid -may probably enable us to judge of the electrical state of the organ -which produces it; as for example, the general redundance of acid -in urine, though secreted from blood that is known to be alkaline, -appears to indicate in the kidney a state of positive electricity; and -since the proportion of alkali in bile seems to be greater than is -contained in the blood of the same animal, it is not improbable that -the secretory vessels in the liver may be comparatively negative. - -781. We may imagine, says Dr. Young, that at the division of a minute -artery a nervous filament pierces it on one side, and affords a pole -positively electrical, and another opposite filament a negative pole. -Then the particles of oxygen and nitrogen contained in the blood, being -most attracted by the positive point, tend towards the branch which is -nearest to it; while those of the hydrogen and carbon take the opposite -channel; and that both these portions may be again subdivided, if it -be required; and the fluid thus analysed may be recombined into new -forms by the reunion of a certain number of each of the kinds of minute -ramifications. In some cases the apparatus may be somewhat more simple -than this; in others, perhaps, much more complicated; but we cannot -expect to trace the processes of Nature through every particular step; -we can only inquire into the general direction of the path she follows. - -782. Considerations such as these afford us a glimpse into the mode in -which Nature conducts some of her most secret and subtile operations; -or rather into the immediate agency by which she effects them; for, -properly speaking, of the mode in which she works, we do not obtain -the slightest insight, and even of her immediate agency our view, at -least in the present state of our knowledge, is indistinct and vague. -By the study of the apparatus which she builds up, we can trace back -her operations a step or two; but in every case, at a certain point, -the apparatus itself becomes so delicate as to elude our senses, and -then of course we are necessarily at a stand. So, the rough materials -with which she carries on her great work of secretion, by careful -analysis we can separate into divers parts, and ascertain that each -part possesses peculiar properties. The main channels by which she -conveys these varied constituents to the different parts of the system -we can trace; the delicate organs by which she produces on these rude -materials her wonderful transformations we can see; but beyond the -threshold of these organs we cannot go. Why from one common mass of -fluid the same variety of peculiar substances are constantly separated, -and each in its respective place: why the kidney never secretes milk, -nor the liver urine, nor the breast bile: why membrane, and muscle, and -bone, and fat, and brain, are uniformly deposited in the same precise -situation: why these depositions go on with uniformity, constancy and -regularity; and by what laws each process is controlled and modified, -we do not know. But though with whatever diligence we investigate these -operations, the great problem remains, and probably ever will remain -unresolved, still it is both a pleasurable and a profitable labour to -follow Nature in her path, to the extreme point to which it is possible -to trace her footstep; for the phenomena themselves are often in the -highest degree curious and interesting; while their order and relation -can seldom be so considered as to be understood, without the suggestion -of practical applications of great and permanent usefulness. - - - - -CHAPTER XII. - -OF THE FUNCTION OF ABSORPTION. - - Evidence of the process in the plant, in the animal—Apparatus - general and special—Experiments which prove the absorbing power of - blood-vessels and membrane—Decomposing and analysing properties - of membrane—Endosmose and exosmose—Absorbing surfaces, pulmonary, - digestive, and cutaneous—Lacteal and lymphatic vessels—Absorbent - glands—Motion of the fluid in the special absorbent vessels—Discovery - of the lacteals and lymphatics—Specific office performed by the - several parts of the apparatus of absorption—Condition of the system - on which the activity of the process depends—Uses of the function. - - -783. Absorption is the function by which external substances are -received into the body, and the component particles of the body are -taken up from one part of the system, and deposited in some other -part. So universal and constant is the operation, that there is not a -fluid nor a solid, not a surface nor a tissue, not an external nor an -internal organ, which is not, in its turn, the seat and the subject of -the process. By its action the component particles of the living body -are kept in a state of perpetual mutation. - -784. The plant in a humid atmosphere increases in weight. The nutritive -matter of the plant diffused in the soil is taken up by its capillary -rootlets, or by the spongolæ which are attached to them, and conveyed -into the system. The fall of dew or rain upon leaves promotes the -growth of the plant. Leaves placed on water are capable of preserving -not only their own vitality, but that of the branches and twigs to -which they are attached. These phenomena show that the process of -absorption is carried on by the plant. - -785. The evidence of the absorbing power possessed by the animal is -still more striking. - -786. 1. If an animal be immersed in water the amount of which is -ascertained by measure, its head being kept out of the water, so that -none can enter the mouth, the body increases in weight and the water -diminishes in quantity. If certain animals, as snails, are plunged in -water impregnated with colouring matter, the fluids in the interior -of their body soon acquire the colour of the water by which they are -surrounded. Frogs, previously kept for some time in dry air, when -placed in water, absorb a quantity equal in weight to their whole body. - -787. 2. In a humid atmosphere the animal increases in weight still more -than the plant. - -788. 3. If a quantity of water be injected into any of the great -cavities of the body, as into that of the peritoneum, the whole of the -fluid after a certain time disappears; it is spontaneously removed. - -789. 4. If in the progress of disease a fluid be poured into any cavity -of the body, as often happens in dropsy, the whole of the fluid is -removed, sometimes spontaneously and quite suddenly; but more often -slowly, under the influence of medicinal agents. - -790. 5. Certain substances, whether applied to an external or an -internal surface, produce specific effects on the system, just as when -they are received into the stomach or injected into the blood-vessels. -Mercury in mere contact with the skin, but more rapidly when the -application is aided by friction, produces the same specific action -upon the salivary glands, and the same general action upon the system -as when the preparation of the metal is received into the stomach. -By the like external and local application arsenic, opium, tobacco, -and other narcotics produce their distinct and peculiar effects on -the nervous system, and their remote and general effects on the other -systems. - -791. 6. If an organ or tissue be deprived of nourishment, it gradually -diminishes in bulk, and at length wholly disappears from the system. -By long-continued pressure, such as that occasioned by the pulsation -of a diseased artery, as in aneurism, or by the growth of a fleshy -tumor, portions of the firmest and strongest muscle, nay, even of the -most dense and compact bone, wholly disappear. At one time the fluids -diminish in quantity, the flesh wastes, and the weight of the body is -reduced one half or more. Under other circumstances, while the state of -the general system remains stationary, some particular part diminishes -in size, or altogether disappears. - -792. 7. Healthy and strong men, engaged in hard labour and exposed to -intense heat, sometimes lose, in the space of a single hour, upwards -of five pounds of their weight. Though daily engaged for months -together in this occupation at two different periods of the day, for -the space of an hour each time, and though consequently these men lose -five pounds twice every day, yet when weighed at intervals of three, -six, or nine months, it is found that the weight of the body remains -stationary, not varying, perhaps, more than a pound or two. It follows -that the bodies of these men must absorb, twice every day, a quantity -equal in weight to that which they lose. - -793. These phenomena depend on a power inherent in the body, that of -taking up and carrying into the system certain substances in contact -with its surfaces, and of transporting from one part of its system to -another its own component particles. - -794. The apparatus by which these operations are carried on is general -and special. - -795. The general apparatus consists of blood-vessels and membrane. The -special apparatus consists of a peculiar system of vessels, namely, -the lacteals and lymphatics, together with the system of glands termed -conglobate. - -796. It is proved by direct experiment that the walls of blood-vessels -exert a power by which substances in contact with their external -surface penetrate their tissue, reach their internal surface, and mix -with the mass of the circulating fluids, and that this property is -possessed by all blood-vessels, arteries and veins, great and small, -dead and living. - -797. If a portion of a vein or artery taken from the body be attached -by either extremity to two glass tubes in order to establish a current -of warm water in its interior, if the vein be then placed in a fluid -slightly acidulated, and the fluid which flows through the vessel be -collected in a flask, this latter fluid becomes, in the space of a few -minutes, sensibly acid. In this experiment there is no possibility -of communication between the current of warm water and the external -acidulated fluid, consequently the latter must penetrate the parietes -of the vessel, that is, absorption must take place through its -membranous walls. - -798. A striking experiment demonstrates the absorbing power of the -living blood-vessels. If the trunk of a vein or artery be exposed in a -living animal, and a poisonous substance in solution be dropped on the -external surface of either, the animal is killed in a few minutes, -just as when the poison is injected into the blood-vessel itself. -Analogous experiments on the minute blood-vessels not only show that -they are endowed with the like absorbing power, but that their number, -tenuity and extent, are conditions which greatly favour the activity of -the process. - -799. Membrane is an organised substance abounding with blood-vessels. -Whether the absorbing power possessed by this tissue be due only to -these vessels, or whether it be assisted in the operation by other -agents not yet fully ascertained, it is certain that the absorbing -power it exerts is highly curious and wonderful. - -800. An animal membrane placed in contact with water becomes saturated -with fluid: placed in contact with a compound fluid, as with water or -spirit holding colouring matter in solution, the membrane actually -decomposes the compound and resolves it into its elementary parts, -just as accurately as can be done by the chemist. If one extremity -of a piece of membrane be placed in a vessel containing the tincture -of iodine, for example, and the other extremity be kept out of the -fluid, that portion of the membrane which is in immediate contact with -the tincture acquires a perfectly dark colour, because the iodine -completely penetrates the substance of the membrane. This dark-coloured -portion is bounded by a definite line, above which the membrane -is penetrated by a different part of the solution, by a pearly, -colourless fluid, the alcohol in which the iodine was suspended. Above -this again there are traces of a still lighter coloured fluid, which -is probably water. In like manner, if strips of membrane are placed in -glasses containing port wine, the same analytical process is effected -by the membrane. The colouring matter of the wine is imbibed by the -lower portion of the membrane; above this is the alcohol, and above -this the water. - -801. These and many analogous experiments demonstrate that the -process of absorption is accompanied with the further phenomena of -decomposition and analysis; and that membrane, at the very moment -it imbibes certain compound substances, resolves them into their -constituent elements. - -802. It is further established by numerous experiments that different -compound substances are decomposed and absorbed by membrane with -different degrees of facility. If strips of membrane are placed in -phials containing different kinds of fluids, one fluid rises only -a line or two; others rise to the height of many inches. There is -indubitable evidence that analogous properties are possessed by living -membrane; that the mucous membrane of the stomach at the moment -it imbibes, decomposes and analyses the alimentary and medicinal -substances in contact with its surface; and consequently that in all -animals membrane becomes a most important agent in carrying on the -digestive process. - -803. But perhaps the most remarkable property possessed by membrane is -that of establishing in fluids in contact with its surfaces currents -through its parietes, which proceed in opposite directions, according -to the different natures of the fluids, and more especially according -to their different densities. If small bladders composed of membrane -are filled with a fluid of greater density than water, and securely -fastened, and then thrown into water, they acquire weight and become -swollen and tense. If the experiment be reversed; if the bladders be -filled with water and immersed in a denser fluid, the denser fluid -flows inwards to the water, and the water passes from the interior -outwards. M. Dutrochet, who was led by accident to the observation -of these phenomena, and who saw at once the possible importance of -this agency in some organic processes hitherto involved in great -obscurity, commenced an extended series of experiments with a view -to ascertain the exact facts. He took the cæca of fowls, membranous -bags already made to his hand, into which he introduced a quantity -of fluid consisting of milk, thin syrup, or gum-arabic dissolved in -water. Having securely tied the membranes, he placed the bags thus -filled in water, and found that two opposite currents are established -through the walls of the cæca. The first and strongest current, that -from without inwards, is formed by the flow of the external water -towards the thicker fluid contained in the cæca; the second and weaker -current, that from within outwards, is formed by the flow of the -thicker interior fluid towards the external water. The first or the -in-going current is termed _endosmose_, from ενδον, intus, and -ωσμος, impulsus, and the second or out-going current is termed -_exosmose_, from a similar combination of Greek words signifying an -impulse outwards. - -804. The velocity and strength of these currents are capable of exact -admeasurement. The amount of endosmose is measured by an apparatus -termed an endosmometer, which consists of a small bottle, the bottom -of which is taken out and the aperture closed by a piece of bladder. -Into this bottle is poured some dense fluid; the neck of the bottle is -closed with a cork, through which a glass tube, fixed upon a graduated -scale, is passed. The bottle is then placed in pure water. The water -by endosmose penetrates the bottle in various quantities according -to the density of the fluid contained in its interior through the -membrane closing its bottom. The dense fluid in the bottle, increased -in quantity by the addition of the water, rises in the tube fitted to -its neck, and the velocity of its ascent is the measure of the velocity -of the endosmose. - -805. The strength of endosmose is measured by a similar apparatus, -in which a tube is twice bent upon itself, and the ascending branch -containing a column of mercury which is raised by the fluid in the -interior of the endosmometer, as the volume of this fluid is increased -by the endosmose. By means of these two instruments it is found that -the velocity and strength of endosmose follow the same law, and that -both are proportionate to the excess of the density of the fluid -contained in the endosmometer above the density of water. By numerous -experiments it is ascertained that by employing syrup of ordinary -density (I. 33) an endosmose is obtained, the strength of which is -capable of raising water more than 150 feet. - -806. But though difference of density is necessary to the production -of endosmose, yet numerous and decisive experiments show that the -different natures of fluids, irrespective of their proportionate -densities, materially influence the activity and energy of the process. -Thus, if sugar-water and gum-water of the same density be placed in -the same endosmometer, the former produces endosmose with a velocity -as seventeen and the latter only as eight. The endosmose produced -by a solution of the sulphate of soda is double that produced by a -solution of the hydro-chlorate of soda of the same density. A solution -of albumen exerts an endosmose four times greater than a solution of -gelatin of the same density. - -807. With organic fluids endosmose goes on without ceasing until the -chemical nature of the fluids becomes altered by putrefaction; but -with alkalies, soluble salts, acids, and chemical agents in general, -the endosmose excited is capable only of short continuance, because -such agents enter into chemical combination with the organic tissue of -the endosmometer, and thus destroy endosmose. - -808. It is remarkable that the direction of the endosmotic currents -produced by vegetable membrane is the exact reverse of that produced -by animal membrane under precisely the same circumstances. Thus oxalic -acid, when separated from water by an animal membrane, invariably -exhibits endosmose from the acid towards the water; when separated -by a vegetable membrane, from the water towards the acid: and the -same is the case with the tartaric and citric acids, and with the -sulphuric, the hydro-sulphuric, and the sulphurous acids. I filled, -says Dutrochet, a pod of the _colutea arborescens_, which being opened -at one end only, and forming a little bag, was readily attached by -means of a ligature to a glass tube, with a solution of oxalic acid, -and having plunged it into rainwater, endosmose was manifested by the -ascent of the contained acid fluid in the tube, that is to say, the -current flowed from the water towards the acid. The lower part of the -leek (_allium porrum_) is enveloped or sheathed by the tubular petioles -of the leaves. By slitting these cylindrical tubes down one side, -vegetable membranous webs of sufficient breadth and strength to be -tied upon the reservoir of an endosmometer are readily obtained. An -endosmometer, fitted with one of these vegetable membranes, having been -filled with a solution of oxalic acid and then plunged into rainwater, -the included fluid rose gradually in the tube of the endosmometer, so -that the endosmose was from the water towards the acid, the reverse -of that which takes place when the endosmometer is furnished with -an animal membrane. Vegetable membrane, then, at least with fluids -containing a preponderance of acid, produces a current, the direction -of which is the exact reverse of that produced by animal membrane. - -809. The bodies of organised beings are composed in great part of -various fluids of different density, separated from each other by thin -septa, precisely the conditions which are necessary to the production -of endosmose. But such conditions never concur in inorganic bodies, -whence inorganic bodies never exhibit endosmotic phenomena. Vegetable -tissue of every kind consists of vast multitudes of aggregated cells -intermingled with tubes. The parietes of these hollow organs are -exceedingly delicate and thin; the organs themselves are at all times -filled with fluids, the densities of which are infinitely various; -consequently, by endosmose and exosmose, mutual interchanges of their -contents incessantly go on; those contents brought into contact by -currents moving now in one direction and now in another, now rapidly -and now slowly intermingle, and in consequence of their admixture -changes in their chemical composition take place. It is by these -powers that water holding in solution nutrient matter diffused through -the soil penetrates the spongeolæ of the capillary rootlets, always -filled with a denser fluid than the water contained in the soil,—that -the energetic motion by which the sap ascends is generated,—that the -ascending sap is attracted into fruits, always of greater density -than the crude sap,—that buds are capable of emptying the tissue -that surrounds them when they begin to grow, and that almost all the -phenomena connected with the motions of fluids in plants, and the -chemical changes which those fluids undergo in consequence of this -admixture, is effected. And there cannot be a question that analogous -phenomena take place in the various cells, cavities, and minute -capillary vessels of the animal body. - -810. It is then established on indubitable evidence that all animal -tissues, without exception, possess an inherent property by which they -are capable of transmitting through their substance certain fluids, and -even solids, convertible into fluids; and that the great agent by which -this transmission is effected is membranous tissue, whether in the form -of blood-vessels or of proper membrane. By virtue of this property -fluids and solids are absorbed, by the animal body, with whatever -surface or organ they are in contact, whether with an external or an -internal surface, or with the eye, the mouth, the tongue, the stomach, -the lungs, the liver, or the heart. - -811. But membrane is so disposed and modified, in different parts of -the body, as to admit of the introduction of fluids and solids from the -exterior to the interior of the system with widely different degrees -of facility. There may be said to be in the human body three great -absorbing surfaces, the pulmonary, the digestive, and the cutaneous, -each highly important, but each endowed with exceedingly different -degrees of absorbing power. - -812. The pulmonary surface, for reasons which will be readily -understood from what has been already stated relative to the structure -of the air vesicles of the lungs, is by far the most active absorbing -surface of the body. The mode in which the air vesicles are formed and -disposed has been shown to be such as to give to the lungs an almost -incredible extent of membranous surface, while the membrane of which -the cells are composed is exceedingly fine and delicate. Moreover, -there is the freest possible communication between all the branches of -the pulmonary vascular system, whether arteries or veins; the distance -between the lungs and the heart is short; the course of the blood -from the pulmonary capillaries to the central engine that works the -circulation is rapid, and the lungs are at the same time close to the -central masses of the nervous system, with which indeed they are placed -in direct communication by nerves of great magnitude and of most -extensive distribution. These circumstances account for the wonderful -rapidity with which substances are absorbed, when placed in contact -with the pulmonary surface, and for the instantaneousness and intensity -of the impression produced upon the system, when the substance thus -introduced is of a deleterious nature. - -813. They also afford an explanation of a phenomenon not to have been -credited without experience of the fact, that innoxious substances, -introduced into the air cells of the lungs in moderate quantities -produce no more inconvenience there than when taken into the stomach. -A single drop of pure water, when in contact near the glottis with the -same membrane that forms the air vesicles of the lungs, excites the -most violent and spasmodic cough, and the smallest particle of a solid -substance permanently remaining there occasions so much irritation -that inevitable suffocation and death result. Yet so different is the -sensibility of this membrane in different parts of its course, that -while at the upper portion of the trachea it will not bear a drop -of water without exciting violent disturbance, in the air vesicles -it tolerates with only slight inconvenience a considerable quantity -even of solid matter. An accident of a nature sufficiently alarming, -which occurred to Dessault, affords a striking illustration of this -curious fact. This celebrated surgeon had to treat a case in which the -trachea and esophagus were cut through. It was necessary to introduce -a tube through the divided esophagus into the stomach, and to sustain -the patient by food introduced in this manner. On one occasion the -tube, instead of being passed through the esophagus to the stomach, -was introduced into the trachea down to the division of the bronchi. -Several injections of soup were actually thrown into the lungs before -the mistake was discovered; yet no fatal, and even no dangerous -consequences ensued. Since that period, in various experiments on -animals, several substances of an innoxious nature have been thrown -into the lungs without producing any inconvenience beyond slight -disturbance of the respiration and cough. The reason is, that after a -short time the substances are absorbed by the membrane composing the -air vesicles, and are thus removed from the lungs and borne into the -general circulating mass. At every point of the pulmonary tissue there -is a vascular tube ready to receive any substance imbibed by it, and to -carry it at once into the general current of the circulation. - -814. Hence the instantaneousness and the dreadful energy with which -poisons and other noxious substances act upon the system when brought -into contact with the pulmonary tissue. A solution of nux vomica -injected into the trachea produces death in a few seconds. A single -inspiration of the concentrated prussic acid kills with the rapidity -of a stroke of lightning. This acid in its concentrated form is so -potent a poison, that it requires the most extreme care in the use of -it, and more than one physiologist has been poisoned by it through -the want of proper precaution while employing it for the purpose of -experiment. If the nose of an animal be slowly passed over a bottle -containing this poison, and the animal happen to inspire during the -moment of the passage, it drops down dead instantaneously, just as -when the poison is applied in the form of liquid to the tongue or the -stomach. The vapour of chlorine possesses the property of arresting -the poisonous effects of prussic acid, unless the latter be introduced -into the system in a dose sufficiently strong to kill instantly; and, -hence, when an animal is all but dead from the effects of prussic acid, -it is sometimes suddenly restored to life by holding its mouth over the -vapour of chlorine. - -815. Examples of the transmission of gaseous bodies through the -pulmonary membrane have been already fully described in the account of -the passage of atmospheric air to the lungs, and of carbonic acid gas -from the lungs, in natural respiration. But foreign substances may be -mixed with or suspended in the atmospheric air, which it is the proper -office of the pulmonary membrane to transmit to the lungs, and may be -immediately carried with it into the circulating mass. Thus, merely -passing through a recently-painted chamber gives to the urine the odour -of turpentine. The vapour of turpentine diffused through the chamber is -transmitted to the lungs with the inspired air, and passing into the -circulation through the pulmonary membrane, exhibits its effects in the -system more rapidly than if it had been taken into the stomach, and -thence absorbed. - -816. Vegetable and animal matter in a state of decomposition generates -a poison, which when diffused in the atmosphere, and transmitted -to the lungs in the inspired air, produces various diseases of the -most destructive kind. The exhalations arising from marshes, bogs, -and other uncultivated and undrained places, constitute a poison of -a vegetable nature, which produces principally intermittent fever -or ague. Exhalations accumulating in close, ill-ventilated, and -crowded apartments in the confined situations of densely-populated -cities, where no attention is paid to the removal of putrefying and -excrementitious matters, constitute a poison chiefly of an animal -nature, which produces continued fever of the typhoid character. It is -proved by fatal experience that there are situations in which these -putrefying matters, aided by heat and other peculiarities of climate, -generate a poison so intense and deadly that a single inspiration -of the air in which they are diffused is capable of producing -instantaneous death; and that there are other situations in which a -less highly concentrated poison accumulates, the inspiration of which -for a few minutes produces a fever capable of destroying life in from -two to twelve hours. In dirty and neglected ships, in which especially -the bilge-water is allowed to remain uncleansed; in damp, crowded, and -filthy gaols; in the crowded wards of ill-ventilated hospitals filled -with persons labouring under malignant surgical diseases, or some forms -of typhus fever, an atmosphere is generated which cannot be breathed -long, even by the most healthy and robust, without producing highly -dangerous fever. - -817. The true nature of these poisonous exhalations is demonstrated by -direct experiment. If a quantity of the air in which they are diffused -be collected, the vapour may be condensed by cold and other agents, and -a residuum of vegetable or animal matter obtained, which is found to -be highly putrescent, constituting a deadly poison. A minute quantity -of this concentrated poison applied to an animal previously in sound -health, destroys life with the most intense symptoms of malignant -fever. If, for example, ten or twelve drops of a fluid containing -this highly putrid matter be injected into the jugular vein of a -dog, the animal is seized with acute fever; the action of the heart -is inordinately excited, the respiration is accelerated, the heat -increased, the prostration of strength extreme, the muscular power so -exhausted, that the animal lies on the ground wholly unable to stir or -to make the slightest effort; and, after a short time, it is actually -seized with the black vomit, identical, in the nature of the matter -evacuated with that which is thrown up by an individual labouring -under yellow fever. It is possible, by varying the intensity and the -dose of the poison thus obtained, to produce fever of almost any type, -endowed with almost any degree of mortal power. These facts, of which -practical applications of the highest utility are hereafter to be made, -may suffice to show the importance of the pulmonary membrane as an -absorbing surface. By the extent and energy of its absorbing power, it -is one of the great portals of life and health, or of disease and death. - -818. The digestive surface is of much less extent than the pulmonary; -it is less vascular; it is further removed from the centre of the -circulating system, and it is covered with a thick mucus, which is -closely adherent to it; hence its absorbing power is neither so great -as that of the pulmonary membrane, nor do noxious substances in contact -with it affect the system so rapidly. An appreciable interval commonly -elapses between the introduction of a poison into the stomach and -its action upon the system. An emetic is commonly a quarter of an -hour before it begins to operate: arsenic itself is generally half an -hour, and sometimes three quarters of an hour, before it produces -any decided effect on the system: but at length a noxious substance, -applied to any part of the digestive membrane is introduced into the -circulating mass and produces its appropriate effects on the system, -just as when it is in contact with the pulmonary tissue. - -819. Over the external surface of the body or the skin, there is spread -a thin layer of solid, inorganic, insensible matter, like a varnish of -Indian rubber. The obvious effect of such a barrier placed between the -external surface of the body and external objects, is to moderate the -entrance of substances from without, and the transmission of substances -from within, that is, to regulate both the absorbing and the exhaling -power of the skin. Hence the comparative slowness with which substances -enter the system by the cutaneous surface; the impunity with which the -most deadly poisons may remain for a time in contact with the skin, -with which prussic acid, arsenic, corrosive sublimate, may be touched -and even handled. The internal surface of the body is protected from -the action of acrid substances introduced into the alimentary canal by -a layer of mucus through which an irritant must penetrate before it can -pain the sentient nerve or irritate the capillary vessel; but were not -a still denser shield thrown over the external surface, pain, disease, -and death must inevitably result from the mere contact of innumerable -bodies, which now are not only perfectly innoxious, but capable of -ministering in a high degree to human comfort and improvement. - -820. Immediately beneath the cuticle is a surface as vascular as it is -sensitive, from which absorption takes place with extreme rapidity. -Poison in very minute quantity introduced beneath the cuticle kills -in a few minutes. Arsenic applied to surfaces from which the cuticle -has been removed by ulceration produces its poisonous effects upon -the system just as surely as when introduced into the stomach. -The poisonous matter of small-pox and of cow-pox placed in almost -inappreciable quantity by the lancet beneath the cuticle produces in a -given time its specific action upon the system. When, in certain states -of disease, with the view of bringing the system rapidly under the -influence of a medicinal agent, the cuticle is removed by a blister, -and the exposed surface is moistened with a solution of the substance -whose action is required, the constitutional effects are developed with -such intensity, that if extreme care be not taken in the employment of -any deleterious substance in this mode the result is fatal in a few -minutes. - -821. The phenomena which have been stated may suffice to illustrate the -absorbing power of the general tissues and surfaces of the body; but -superadded to this, there is carried on in particular parts of the -system a specific absorption for which a special apparatus is provided. - -[Illustration: Fig. CXCII. - - An enlarged view of an absorbent vessel.—1. External surface, with the - jointed appearance produced by the valves.—2. The same vessel laid - open, showing the arrangement of the valves.] - -822. The special apparatus of absorption, commonly termed the proper -absorbent system, consists of the lacteal and lymphatic vessels and of -the conglobate glands. The lacteals arise only from the intestines; the -lymphatics, it is presumed, from every organ, tissue, and surface of -the body. Both sets of vessels possess a structure strikingly analogous -to that of veins, the common agents of absorption. The coats of the -lacteals and lymphatics are somewhat thinner and a good deal more -transparent than those of veins; yet thin and delicate as they are, -they possess considerable strength, for they are capable of bearing, -without rupture, injections which distend them far beyond their natural -magnitude. - -823. When fully distended, these vessels present a jointed appearance -somewhat resembling a string of beads (fig. CXCII. 1). Each joint -indicates the situation of a pair of valves (fig. CXCII. 2). These -valves are of a semilunar form, and are composed of a fold of the inner -coat of the vessel (fig. CXCII. 2). The convex side of the valve, in -the lacteals, is towards the intestines; in the lymphatics towards the -surfaces; in both towards the origins of the vessels. The valves allow -the contents of the vessels to pass freely towards the main trunk of -the system, but prevent any retrograde motion towards the origins of -the vessels. - -824. By continued pressure the resistance of the valves may be -overcome, so that mercury may be made to pass from the trunk into the -branches. When this is done in an absorbent trunk proceeding from -certain organs, such as the liver, it is seen that the absorbents are -distributed, arborescently, in such vast numbers that the surface of -the viscus appears as if it were covered with a reticular sheet of -quicksilver. - -825. The internal coat of the small intestines has been shown to -present a fleecy surface, crowded with minute elevations called villi, -which give this surface an appearance closely resembling the pile of -velvet. Each villus consists of an artery, a vein, a nerve, and a -lacteal, united and sustained by delicate cellular tissue. After a meal -the lacteals become so turgid with chyle that they completely conceal -the blood-vessels and nerves, so that the surface of the intestine -presents to the eye only a white mass, or a surface thickly crowded -with white spots (fig. CXCIII.) - -[Illustration: Fig. CXCIII. - - Appearance of the lacteals turgid with chyle, as seen in the jejunum - some time after a meal.] - -[Illustration: Fig. CXCIV. - - Magnified view of two ampullulæ turgid with chyle, terminating the - lacteal vessels.] - -826. When a portion of the intestine in this condition of the lacteal -vessels is examined under the microscope, there is said to be visible -on the villus an oval vesicle, termed an ampullula (fig. CXCIV.). This -vesicle is described as having an aperture at its apex, which it is -conceived constitutes the open mouth of the lacteal, and through which -the chyle is supposed to be taken up. - -[Illustration: Fig. CXCV. - - View of villi, with the lacteals arising from their surface by open - mouths and forming radiated branches. The surface of one of these - villi is represented as entirely white, from the lacteals being so - turgid with chyle as completely to obscure their orifices and their - radiating branches.] - -827. Mr. Cruikshank, who particularly devoted himself to the study of -this part of the absorbent system, states that he had an opportunity -of examining these vessels in a person who died suddenly some hours -after having taken a hearty meal, and who had been previously in sound -health. “In some hundred villi,” he says, “I saw the trunk of the -lacteal beginning by radiated branches (fig. CXCV.). The orifices of -these radii were very distinct on the surface of the villus as well -as the radii themselves (fig. CXCV.). There was but one trunk in each -villus. The orifices on the villi of the jejunum, as Dr. Hunter said -(when I asked him as he viewed them in the microscope how many he -thought there might be) were about fifteen or twenty in each villus, -and in some I saw them still more numerous” (fig. CXCV.). - -828. The course of the lacteals, from their origin in the villi to -their termination in the thoracic duct, has been traced (687). It is -conjectured that the lymphatics take their origin from every point of -the body, but it is admitted that they have not been actually seen -even in every organ; still they have been found in so many that it is -inferred that they really exist in all, and that in those in which they -have not been hitherto detected they have eluded observation on account -of their extreme delicacy and transparency and our imperfect means of -examining them. - -829. Though, like veins, lymphatics anastomose freely with each other, -yet they do not proceed from smaller to larger branches and from larger -branches to trunks, but continue of nearly the same magnitude from -their origin to their termination. They are disposed in two sets, one -of which always keeps near the external surface of the body, and the -other is deeply seated, accompanying more especially the great trunks -of the blood-vessels. - -[Illustration: Fig. CXCVI. - -Fig. CXCVII. - -Fig. CXCVIII. - - CXCVI.—1. Trunks of absorbent vessels entering a gland. 2. Gland laid - open. 3. Highly magnified views of the cells or follicles of which - the gland is supposed to consist. CXCVII.—1. Absorbent vessels called - vasa inferentia, entering (2) the gland. 3. Absorbent vessels emerging - from the gland, called vasa efferentia, and forming (4) a common - trunk. - CXCVIII.—1. Trunk of absorbent vessel entering a gland. 2. Gland - apparently composed entirely of convoluted vessels. 3. Vessels - emerging from the gland and forming (4) a common trunk.] - -830. In the human body every vessel that can be distinctly recognised -either as a lacteal or a lymphatic, passes, in some part of its course, -through a conglobate or lymphatic gland (figs. CXCVII., CXCVIII.). -These glands, small, flattened, circular or oval bodies, resembling -beans in shape, are enclosed in a distinct membranous envelope. Their -intimate structure has been already fully described (chap. xi.). They -are of various sizes, ranging from three to ten lines in diameter: they -are placed in determinate parts of the body, and are grouped together -in various ways, being sometimes single, but more often collected -in masses of considerable magnitude. Numerous absorbent vessels, -termed vasa inferentia, enter the gland on the side remote from the -heart (figs. CXCVII. 1 and CXCVIII. 1); a smaller number, called vasa -efferentia, leave it on the side proximate to the heart (fig. CXCVII. -3). If mercury be injected into the vasa inferentia (fig. CXCVI.), it -is seen to pass into a series of cells of the corresponding gland (fig. -CXCVI. 3), and then to escape by the vasa efferentia; but if the gland -be more minutely injected, as by wax, all appearance of cells vanishes; -the whole substance of the gland seems then to consist of convoluted -absorbents (fig. CXCVIII. 2), irregularly dilated, and communicating -with each other so intimately that every branch that leaves the gland -appears to have been put in communication with every branch that -entered it (fig. CXCVIII. 1, 2, 3). - -831. The motion of the fluid within the absorbent vessels, though not -rapid, is energetic. If a ligature be placed around the thoracic duct -in a living animal, the tube will swell and ultimately burst, from the -rupture of its coat, in consequence of the force of the distension -that takes place below the ligature. If the thoracic duct in the neck -of a dog be opened some hours after the animal has taken a full meal, -the chyle flows from the vessel in a full stream, and in the space -of five minutes half an ounce of the fluid may be obtained. Yet this -system of vessels is beyond the influence of the circulating blood: it -has no heart to propel it; no current behind always in rapid motion -to urge it onwards; it is therefore inferred that it is moved by a -vital contractile power inherent in the vessels, analogous to, if not -identical with, muscular contractility. The flow of blood through the -arterial tubes is universally believed to be effected, in part at -least, by such a contractile power, for this, among other reasons, that -if in a living animal the trunk of an artery be laid bare, the mere -exposure of it to the atmospheric air causes it to contract to such -a degree that its size becomes obviously and strikingly diminished -(298.1). The same phenomenon has been observed in the main trunk of -the absorbent system. Tiedemann and Gmelin state that in the course of -their experiments they saw the thoracic duct contract from exposure to -the air. - - -832. The delicacy and transparency of the lacteals and lymphatics -long concealed them from the view of the anatomist. The lacteals had -indeed been occasionally seen in ancient times, but their office -was altogether unknown. In the year 1563 Eustachius discovered the -thoracic duct, but did not perceive its use. About half a century -afterwards, in the year 1622, the lacteals were again one day by -chance seen by Asellius, in Italy, while investigating the function of -certain nerves. Mistaking the lacteals for nerves, he at first paid no -attention to them; but soon observing that they did not pursue the same -course as the nerves, and “astonished at the novelty of the thing,” he -hesitated for some time in silence. Resolving in his mind the doubts -and controversies of anatomists, of which it chanced that he had been -reading the very day before, in order to examine the matter further, -“I took,” he says, “a sharp scalpel to cut one of these chords, but -scarcely had I struck it when I found a liquor white as milk, or rather -like cream, to leap out. At this sight I could not contain myself for -joy; but turning to the by-standers, Alexander Tadinus and the senator -Septalius, I cried out Εὕρηκα! with Archimedes; and at the -same time invited them to look at so rare and pleasing a spectacle; -with the novelty of which they were much moved. But I was not long -permitted to enjoy it, for the dog now expired, and, wonderful to -tell, at the same instant the whole of that astonishing series and -congeries of vessels, losing its brilliant whiteness, that fluid being -gone, in our very hands, and almost before our eyes, so evanished and -disappeared that hardly a vestige was left to my most diligent search.” -The next day he procured another dog, but could not discover the -smallest white vessel. “And now,” he continues, “I began to be downcast -in my mind, thinking to myself that what had been observed in the first -dog must be ranked among those rare things which, according to Galen, -are sometimes seen in anatomy.” But at length recollecting that the dog -had been opened “athirst and unfed,” he opened a third “after feeding -him to satiety; and now everything was more manifest and brilliant -than in the first case.” The zeal with which he followed out the clue -he had obtained is indicated by the number of dogs, cats, iambs, hogs, -and cows which he dissected, and by the statement that he even bought -a horse and opened it alive; but, he adds, “a living man, however, -which Erasistratus and Herophilus of old did not fear to anatomize, I -_confess_ I did not open.” - -833. Nearly thirty years elapsed before the lacteals, which were long -thought to terminate in the liver, were traced to the thoracic duct; -and it was not until the year 1651, about eighty years after the -discovery of Asellius, that the lymphatics were discovered, and that -the whole of this portion of the absorbent system was brought to light. - -834. Taking together the whole of the apparatus of absorption, the -specific office performed by its several parts seems to be as follows:— - -835. 1. It is established that the lacteals absorb chyle, and that they -refuse to take up almost every other substance which can be presented -to them. Experimentalists are uniform in stating that however various -the substances introduced into the stomach, it is exceedingly rare to -find in the lacteals anything but chyle. These vessels appear to be -endowed with a peculiar sensibility, derived from the nervous system, -by which they are rendered capable of exerting an elective power, -readily absorbing some substances and absolutely rejecting others. - -836. 2. The lymphatics absorb a far greater variety of substances -than the lacteals, but not all substances indiscriminately; chiefly -organized matter in a certain stage of purification; particles passing -through successive processes of refinement (707). - -837. 3. The blood-vessels, and more especially the capillary veins, -appear to absorb indiscriminately all substances, however heterogeneous -their nature, which are dissolved or dissolvable in the fluids -presented to them. - -838. 4. The absorbent glands appear by various modes, either by -removing superfluous and noxious matters, or by the addition of -secreted substances possessing assimilative properties, to approximate -the fluid which flows through them more and more closely to the nature -of the blood. Fatal effects result from the artificial infusion of -minute portions even of mild substances into the blood. Hence the -extended and winding course which Nature causes the new matter formed -from the food to undergo, even after its elaboration in the digestive -apparatus, in order that, before it is allowed to mingle with the -blood, its perfect purification and assimilation may be secured. - -839. The activity or inactivity of the process of absorption is mainly -dependant on the emptiness or the plethora of the system. There is -a point of saturation beyond which the absorbent vessels, though in -immediate and continued contact with absorbable matters, will take -up no more. The nearer the system to this point the less active the -process; the further the system from this point the more active the -process. Thus, when an animal whose vessels are full to saturation is -immersed in water, or exposed to humid air, its body does not increase -in weight, and there is no sensible diminution of the water; but the -longer an animal is kept without fluid, and the more it is exposed -to the action of a dry air, the further its system is removed from -the point of saturation, and exactly in that proportion, when it is -brought in contact with water, is the diminution of the quantity of the -fluid and the increase in the weight of the body. This law explains -many circumstances of the animal economy,—why it is impossible to -dilute the blood or any other animal fluid beyond a certain point, -by any quantity of liquid which may be in contact with the external -surface, or which may be taken into the stomach; why it is impossible -to introduce nutrient matter into the system, beyond a certain point, -by any quantity of food, which the digestive organs may convert into -chyle; why, consequently, the bulk and weight of the body are incapable -of indefinite increase; why that bulk and weight are so rapidly -regained after long abstinence; and why the appetite is so keen, and -the ordinary fulness and plumpness of the body are so soon restored, -after recovery from fever and other acute diseases, when the digestive -organs have been uninjured. - -840. Different portions of the absorbent apparatus accomplish specific -uses. With the absorbent action of the capillary blood-vessels and of -membranous surfaces every organic function, but more especially the -processes of digestion and respiration, are intimately connected. - -841. The specific absorption carried on by the lacteals has for its -object the introduction of new materials into the system, for the -reparation of the losses which it is constantly sustaining by the -unceasing actions of life. - -842. The specific absorption carried on by the lymphatics has a -two-fold object. First, the introduction of particles, which have -already formed an integrant part of the system, a second time into the -blood, in order to subject them anew to the process of respiration, -thereby affording them a second purification, and giving them new and -higher properties; and, secondly, the regulation of the growth of the -body, and the communication and preservation of its proper form. - -843. It is the office of the lacteals to replenish the blood by -constantly pouring into it new matter, duly prepared for its conversion -into the nutritive fluid. It is the office of the lymphatics to preside -over the distribution of the blood as it is deposited in the system in -the act of nutrition. The lymphatics are the architects which mould and -fashion the body. They not only regulate the extension of the frame, -but they retain each individual part in its exact position, and give to -it its exact size and shape. Growth is not mere accretion, not simple -distension; it consists of a specific addition to every individual -part, while all the parts retain the same exact relation to each other -and to the whole. When a bone grows it does not increase in bulk by -the mere accumulation of bony matter; but every osseous particle is so -increased in length and breadth that the relative size of every part, -and the general configuration of the whole organ, remain precisely -the same. When a muscle grows, while the entire organ enlarges in -bulk by the augmentation of every individual part, each part retains -exactly its former proportions and its relative connexions. When the -brain grows a certain quantity of cerebral matter is added to every -individual part, but at the same time the proportionate size and -original form of each part, and the primitive configuration of the -entire organ, are retained exactly the same. How is this effected? By -a totally new disposition of every integrant particle of every part of -every organ. New matter is not deposited before the removal of the old: -the lymphatic, in the very act of removing the old, fashions a mould -for the reception of the new, and then the capillary artery brings -the new particle and deposits it with unerring exactness in the bed -prepared for it. Thus, by removing the old materials of the body in a -determinate manner, and thereby fashioning a mould for the reception of -the new, the lymphatics may be said, in the strictest sense, to be the -architects of the frame. - - - - -CHAPTER XIII. - -OF THE FUNCTION OF EXCRETION. - - In what excretion differs from secretion—Excretion in the - plant—Quantity excreted by the plant compared with that excreted - by the animal—Organs of excretion in the human body—Organization - of the skin—Excretory processes performed by it—Excretory - processes of the lungs—Analogous processes of the liver—Use of the - deposition of fat—Function of the kidneys—Function of the large - intestines—Compensating and vicarious actions—Reasons why excretory - processes are necessary—Adjustments. - - -844. The various matters contained in organized bodies, and even -those which enter as constituent elements into their composition, are -constantly removed from the system, and thrown off into the external -world. The matters thus rejected are called excretions; and the various -processes by which their elimination is effected constitute a common -function termed excretion. - -845. Excretion is the necessary consequence of the deterioration which -all organized matter undergoes by the actions of life. The matters -removed by the process consist of the waste particles of the body, or -the particles expended in the vital actions, as the aliment contains -the particles which replenish the waste, and compensate the expenditure. - -846. The excretions are separated from the common organized mass by -processes perfectly analogous to those comprehended in the great -function of secretion. Excretion is only a particular form of -secretion: the difference between the two functions is, that, in the -former, the matter eliminated being either noxious or useless, is -separated for the sole purpose of being rejected; while, in the latter, -the matter eliminated is destined to perform some useful purpose -in the economy. Accordingly, the products of excretion are termed -excrementitious; and those of secretion, recrementitious. - -847. The chief matters excreted by the plant are oxygen, carbonic acid, -air; water, in some few cases, under peculiar circumstances, ammonia -and chlorine; and in still rarer cases, during the night, poisonous -substances, as carburetted hydrogen, together with acrid, and even -narcotic principles. - -848. The forms under which these excretions are eliminated are -exceedingly various. Sometimes the matter excreted is in the shape of -gas, at other times it is in that of vapour, and at others in that of -liquid. The chief gaseous exhalations are oxygen and carbonic acid; -the vaporous exhalations consist principally of water, in the state -of vapour; and the liquid exhalations are either pure water, or water -holding in combination sugar, mucilage, and other proximate vegetable -principles. Even the peculiar products formed by the vital actions -of the plant, as the volatile oils, the fixed oils, the balsams, the -resins, and perhaps, with the exception of gum, sugar, starch, and -lignine, all the substances formed out of the proper juices of the -plant, are true excretions; for these substances are fixed immovably -in the cells, sacs, or tubes which secrete and contain them: they are -not consumed in the growth of the plant; they do not appear to be -applied to any useful purpose in the economy; they are injurious, and -even poisonous to the very plant in which they are formed when taken up -by the roots and combined with the sap: as long as they remain in the -plant they are isolated in the individual parts in which they are first -deposited, until with the advancing age of the plant they lose their -aqueous particles, and are finally dried up; they, therefore, possess -all the essential characters of excrementitious substances. - -849. The organs by which these matters are excreted are the leaves, the -flowers, the fruits, the roots, and certain bodies called glands. - -850. The gaseous and vaporous exhalations are effected chiefly by the -leaves, which it has been shown (320 and 465), under the influence of -the solar ray, are always pouring out a large quantity of oxygen, and -still larger quantities of fluid in the state of vapour. - -851. Similar matters are exhaled by the flowers either in the form -of vapour or of liquid; and this exhalation commonly bears with it -a peculiar odour, which proceeds from an essential oil, sometimes -evaporated with the pollen, and at other times secreted by glandular -bodies which have their seat in the petals. - -852. Fruits, and especially green fruits, as raspberries, pears, -apples, plums, apricots, figs, cherries, gooseberries, and grapes, pour -out oxygen during the day, and carbonic acid gas during the night, and -thus co-operate with leaves in carrying on the function of excretion. - -853. The more elaborate excretions contained in special receptacles, -and formed by diverse organs from the proper juices of the plant, -descend chiefly by the bark, and are poured by the roots into the soil. -These excretions, if re-absorbed by the roots, and re-introduced into -the system of the plant that has rejected them, poison that plant. -Consequently, two processes of deterioration are always going on in the -soil; first, the absorption of the nutrient matter contained in it; -and, secondly, the accumulation of excrementitious matter constantly -poured into it by the growing plant. By the addition of manure, the -soil is replenished with fresh nutritive materials; by a rotation of -crops, it is purified from noxious excretions. It is a remarkable -and beautiful adjustment, that excrementitious substances which are -destructive to plants of one natural family, actually promote the -growth of plants of a different species. Thus, if wheat be sown upon -a tract of land proper for that grain, it may produce a good crop the -first, the second, and perhaps even the third year, as long as the -ground is what the farmers call in good heart. But, after a time, it -will yield no more of that particular kind of corn. Barley it may still -bear, and, after this, oats, and perhaps after these, pease, or some -other species belonging to a different family. The excrementitious -matter deposited in the soil by a preceding is absorbed by a succeeding -crop; the matter excreted by the former serving as nutriment or -stimulus to the latter. But though in this mode all noxious matter is -removed from the soil, yet the ground at last becomes quite barren, in -consequence of having parted with all its nutrient particles, and then -it will yield no more produce until it is supplied with a new fund of -matter. This new matter is afforded by vegetable or animal substances, -in which, the principle of life having become extinct, the peculiar -bond that held their particles together is dissolved. Leaves, flowers, -fruits, bark, roots; hair, skin, horns, hoofs, fat, muscle, bone, the -blood itself, whatever has formed a part of the organized body, now -dead, and repassing through the process of decomposition, back to the -simple physical elements, all its forms of beauty gone, and exhaling -only matters highly deleterious to animal life, mixed with the soil, -are recombined into new products, spring up into new plants, and thus -re-appear under new forms of beauty, and afford fresh nutriment to -myriads of animals. The very refuse of the matters which have served as -food and clothing to the inhabitants of the crowded city, and which, -allowed to accumulate there, taint the air, and render it pestilential, -promptly removed, and spread out on the surface of the surrounding -country, give it healthfulness, clothe it with verdure, and endow it -with inexhaustible fertility. - -854. The quantity of matter excreted by the plant is proportionate to -the energy of its vital actions. Hence it is always greatest in spring, -when the tender leaves are beginning to shoot; gradually diminishes as -autumn approaches; and, at last, as the leaves turn yellow, and the -vessels which connect the leaves with the stalk dry up and are closed, -it almost wholly ceases. - -855. It is copious in proportion to the number of the leaves, and to -the extent of the surface they present. From experiments performed as -long ago as the year 1699, by Woodward, it appears that, of the whole -quantity of water absorbed by the plant, the least proportion exhaled -to that retained is as 46 or 50 to 1; in many cases it is as 100 or 200 -to 1, and in some above 700 to 1. In one experiment, a plant which -imbibed 2501 grains of water, increased in weight only three grains -and a half: hence the dampness and humidity of the air in all places -in which trees and the larger vegetables abound; more especially when -the leaves are young, and most numerous and active; and hence also the -magnitude of the rivers in all extensive countries which are covered -with forests. - -856. Exhalation, scarcely appreciable in the night, is most abundant -during the day under the influence of the solar light. If two plants -of the same size are covered with two glass bells, and one be exposed -to the sun’s light, while the other is left in the shade, the inner -surface of the former bell becomes covered with drops of water, while -that of the second remains perfectly dry. - -857. The absolute quantity of matter excreted by the plant is widely -different in different species. According to Hales, in a sun-flower -three feet and a half high, the leaves of which presented a surface -of 5616 square inches, or 39 square feet, the greatest quantity -exhaled in twelve hours, during the day, was one pound fourteen -ounces avoirdupois; the medium quantity one pound four ounces. In a -middle-sized cabbage, the greatest quantity exhaled was one pound -nine ounces; the medium quantity one pound three ounces. In a vine, -the greatest quantity exhaled was six ounces; the medium quantity -five ounces. In a young apple tree having 163 leaves, the surface -of which was equal to 1589 square inches, or 11 square feet, the -greatest quantity exhaled was eleven ounces; the medium quantity nine -ounces. Martino calculated the quantity exhaled by a cabbage, in the -twenty-four hours, at twenty-three ounces; by a young mulberry-tree, -eighteen ounces; and, by a maize plant, seven drachms. - -858. Supposing the weight of the human body to be 160 pounds, and -the weight of a sun-flower 3 pounds, the relative weights of the two -bodies will be as 160 to 3, or as 53 to 1. The surface of such a human -body is equal to 15 square feet, or 2160 square inches; the surface -of the sun-flower is 5616 square inches, or as 26 to 10. The quantity -perspired in the twenty-four hours by an ordinary-sized man, according -to the estimate of Keill, is about thirty-one ounces. Allowing two -ounces for the exhalation during the beginning and the ending of -the night, the quantity exhaled by the plant, in the same time, is -twenty-two ounces; so that the perspiration of a man to that of a -sun-flower is nearly as 141 to 100, though the weight of the man to -that of the sun-flower is as 53 to 1. Taking bulk for bulk, the plant -imbibes seventeen times more fresh fluid than the man, partly, no -doubt, for the reason assigned by Hales—because, “the fluid which is -filtered through the roots of the plant is not near so full freighted -with nutrient particles as the chyle which enters the lacteals of the -animal; the plant, therefore, requires a much larger supply of fluid.” - -859. As soon in the animal series as organs are formed distinct from -the homogeneous mass of which the minute and simple beings placed -at the bottom of the scale appear to consist, these organs are -appropriated, at least in part, to the function of excretion. In the -human being, six organs take a part, and are chiefly appropriated to -this function—namely, the skin, the lungs, the liver, the adipose -tissue, the kidneys, and the intestinal canal. All these organs serve -other purposes in the economy; but still the removal, in some specific -form, of excrementitious matter from the system, is a most important -part of the office of each. - -860. The skin (34), to which are assigned numerous and highly important -offices, seems to be specially constructed for performing the function -of excretion. It is composed of three layers, of which the internal -is called the cutis, or true skin; the external the cuticle, or scarf -skin; and the middle, by which the other two are united, the rete -mucosum. The latter is indistinct, excepting in the negro, in whom it -is the seat of colour. - -861. The cutis, or true skin, is a dense membrane, composed of firm -and strong fibres, interwoven like a felt. Its internal surface is -marked by numerous depressions, which receive processes of the adipose -tissue beneath. Over its external surface is spread a delicate and -complex net-work of vessels, termed the vascular plexus, of such -extent and capacity that, in the natural state of the circulation, a -very large proportion of the whole blood of the body is constantly -flowing in these blood-vessels of the cutis. A prodigious number of -nerves accompany the cutaneous blood-vessels, some derived from the -organic, and others from the sentient portion of the nervous system. -The organic nerves endow the arteries with the power of performing -the organic processes proper to the cutis, which are principally of -an excrementitious nature. The sentient nerves communicate to every -point of the external surface of the cutis the exquisite degree of -sensibility possessed by the skin. Innumerable absorbent vessels -terminate at the same points, with the capillary arteries and the -sentient nerves. - -862. The extreme smoothness and softness natural to the skin is -communicated to it by a number of follicles which are placed in the -cutis, and are termed sebaceous, from the oily substance they secrete. -It is the matter secreted by these organs which communicates to the -animal body the odour peculiar to it, on which the scent depends. - -863. In many parts the cutis is perforated obliquely by hairs, which -spring from little bulbs beneath it, to which the growth of the hairs -is confined. The human hair, which is hollow, consists of fine tubes -filled with an oily matter. This matter is either of a black, red, -yellow, or pale colour, as the hair is black, red, yellow, or white. - -864. The nails are products formed by the cutis, and are essentially -the same as the cuticle. - -865. By long-continued boiling the cutis is resolvable into gelatin, -which by evaporation becomes glue, and by combining with tannin and the -extractive of oak bark is converted into leather. - -866. The third portion of the skin, the cuticle, is a thin, elastic -membrane spread over the external surface of the cutis, from which it -is easily detached, by the action of a blister in the living, and by -the process of putrefaction in the dead body. It is without vessels and -nerves, and consequently it is insensible and inorganic. It is formed -as a secretion by the cutis, and is composed almost entirely of solid -albumen. When any portion of it is removed, it is renewed with great -rapidity. Since it is subject to constant waste from friction, and is -much increased by pressure, as is manifest in the palms of the hands -and the soles of the feet, its formation must be continual; yet even in -the fœtus it is thicker in the parts where pressure is ultimately to be -made than in the other parts of the body. - -867. The cuticle is a sheath in which the body is enclosed for the -purpose of restraining the organic actions which take place at its -surface, and for tempering the sentient impressions received there. For -restraining the organic actions it is fitted by the cohesion of its -parts, which is such as to receive and transmit any fluid very slowly, -as is manifest from the dryness of its surface when it is raised in -a blister, and from the extreme rapidity with which the cutis dries, -until it becomes as hard as parchment, when the cuticle is removed from -it in the dead body. - -868. Diffused over every part and particle of the cutis is the seat -of common sensation, that cognizance may be taken of the presence of -external objects. Restricted to particular points, the tips of the -fingers, is the seat of one of the special senses, that of touch. -Had the nerves which communicate to this extended surface its acute -sensibility been placed in direct contact with external bodies, -intolerable pain would have been the result; but by covering this -surface with an inorganic and insensible substance, yet so thin that it -is a pellicle rather than a membrane, the organ of sense is shielded, -while the delicacy of the sensation is not impaired. But the control -of the organic process and the protection of the sentient nerve are -not the only offices performed by the cuticle; it serves further to -hide what it is undesirable to have constantly in view. All that is -beautiful in the blood as an object of sense is rendered visible -through the cuticle, in the bright and rosy hue of health, at the same -time that every process, the sight of which would excite anxiety or -terror, is effectually concealed. - -869. The skin, an organ of secretion, an organ of absorption, an organ -of excretion, and an organ of sense, is thus the immediate seat of -three organic processes and of one animal process. - -870. The chief excretion performed by the skin, in the human body, is -commonly known under the name of perspiration. The perspiration is -either sensible or insensible. Sensible perspiration is the liquid -commonly called the sweat. Insensible perspiration consists of a vapour -which, under the ordinary circumstances in which the body is placed, -is invisible. The invisible vapour is constantly exhaling; the visible -liquid is only occasionally formed. The quantity of matter carried out -of the system under the form of invisible vapour is much greater than -that lost by the visible liquid. - -871. That a quantity of matter is incessantly passing off from the -surface of the skin, under the form of an invisible vapour, is proved -by the following facts:— - -1. If the hand and arm are enclosed in a glass jar, the inner surface -of the glass soon becomes covered with moisture. - -2. If the tip of the finger be held at about the twelfth of an inch -from a mirror, or any other highly polished surface, the surface -rapidly becomes dimmed by the vapour which condenses upon it in small -drops, and which disappear on the removal of the finger. - -3. If the body be weighed at different periods, an accurate account -being taken of the ingesta and the egesta, it is found to undergo a -loss of weight sensibly greater than can be attributed to any of the -visible discharges: this loss must be owing to the transmission of a -quantity of matter out of the body, under the form of invisible vapour. - -872. The matters excreted under the form of perspiration are separated -from the blood by a true and proper secretion, like the other -secretions of the body. The process by which this is effected is called -transudation. The matter of transudation deposited on the surface of -the skin by a vital function is removed from the body by evaporation, -a physical process which consists of the conversion of a liquid -into a vapour by the addition of heat. Consequently the process of -perspiration is a cooling process, and it is chiefly by the increase of -the perspiration that the body is enabled to bear the intense degrees -of heat which it has been shown (491, _et seq._) to be capable of -sustaining. Sitting one day in repose in the shade during the intense -heat of an American summer’s day, the skin freely perspiring at every -pore, Dr. Franklin happened to examine the temperature of his body with -a thermometer. He found that the temperature of his body was several -degrees lower than that of the surrounding air. The physiologists who -exposed themselves in heated chambers, for the sake of ascertaining the -greatest degree of heat which the human body is capable of enduring, -perspired profusely during the experiment (495). The artisans who -carry on their daily occupations in elevated temperatures perspire -most profusely (884, _et seq._). Under such circumstances, caloric is -communicated to the human body just as freely as to inorganic matter -yet it does not injure the body, because it does not accumulate in the -system, but is immediately expended in supplying the heat necessary -to convert the water, which is poured out upon the skin, into vapour. -In this manner that surface of the body at which, under ordinary -circumstances, a large portion of its animal heat is generated, is -the very surface at which, under extraordinary circumstances, cold is -generated, and the heat of the system positively reduced. - -873. The physical process of evaporation would go on to a certain -extent, though the vital function of transudation did not exist, and -does go on in the dead body when the vital function is at an end. An -organic tissue enclosing a liquid may not be porous enough to give -passage to a single drop of liquid, and yet sufficiently porous to -admit air. In this case the air in contact with the tissue dissolves -the liquid in its interior, and carries it off in the form of invisible -vapour; hence liquids contained in organic bodies in contact with the -air diminish in quantity by evaporation. But if an animal be placed -in air saturated with moisture, and of the same temperature as its -own, the air can no longer deprive that animal of a single particle of -its moisture: evaporation from the body, in such a condition of the -air, is suppressed. On the other hand, when an animal is placed in -air saturated with moisture, and of the same temperature as its own, -so far is transudation from being suppressed, that the sweat streams -from every part of the external surface of the body. By modifying -the condition of the air, in regard to its hygrometrical state and -its temperature, the result of the physical process and of the vital -function may thus be separated from each other, and the amount of each -may be ascertained with perfect exactness. Now, by numerous experiments -on the cold-blooded vertebrata, placed under such conditions of the -air, it is found that, in these animals, perspiration by evaporation is -to that by transudation as 6 to 1. But since the human body presents to -the air an immense extent of surface over which is constantly flowing -a large proportion of the whole quantity of blood contained in the -system, the loss by the physical process compared with that by the -vital function must be still greater in man than in the cold-blooded -animal. - -874. Taking together the average quantity of matter removed from -the human body by both processes, or the whole loss of weight -sustained from perspiration, on the comparison of the results of -many observations, it is estimated to vary from twenty ounces in the -twenty-four hours of the colder, to forty ounces in the warmer climates -of Europe. Keill estimated it at thirty-one ounces. In the climate of -Paris it is stated to be thirty ounces. - -875. By the delicate tests of modern chemistry, various substances are -found to be contained in the aqueous fluid which constitutes the great -proportion of the matter of perspiration, namely, an acid, probably the -lactic, a small proportion of animal matter, some alkaline and earthy -salts, an oily or fatty substance, probably derived from the sebaceous -follicles. All these matters are so analogous to the constituents of -the serum of the blood as to leave little ground for doubt that they -are merely separated from this part of the blood as it is flowing -through the complex net-work of vessels spread over the surface of the -cutis (861). - -876. The skin, when in contact with the air, also separates a portion -of carbon from the blood, and to the extent in which it does this it -is auxiliary to the lungs; but the quantity of carbonic acid excreted -by the skin is small and variable in amount. The primary office of -the skin as an organ of excretion is to relieve the blood of its -superabundant watery particles, that is, to remove from the system its -superfluous hydrogen. - -877. A full account has been given (359, _et seq._) of the primary -office of the lungs, which, it has been shown, is to decarbonize the -blood. The details of the calculations have been stated (457), from -which it is estimated that 10 ounces and 116 grains of carbon are daily -exhaled by the lungs under the form of carbonic acid; and the reasons -have been assigned which favour the conclusion that the carbonic acid -expired is not formed immediately in the lungs by the combination of -the oxygen of the atmospheric air with the carbon of the blood; but in -the system, where the oxygen taken into the blood at the lungs unites -with carbon, the carbonic acid resulting from the combination passing -as soon as formed into the capillary veins. The blood contained in -these vessels, thus become venous, returns to the lungs, where it gives -off the carbonic acid accumulated in it, and by that depuration again -assumes its arterial character. - -878. Some interesting experiments performed by Dr. Stevens appear -to show that there exists a powerful attraction between oxygen and -carbonic acid, and that the venous blood, as it is flowing through the -lungs, is freed from its carbonic acid by virtue of that attraction. -Chemists were so universally agreed that the carbon in carbonic acid is -united with its maximum dose of oxygen, that the idea of an attraction -between carbonic acid and oxygen appeared highly improbable. The -evidence of the fact, however, is decisive. If a receiver, filled with -carbonic acid, and closed by a piece of bladder, firmly tied over it, -be exposed to the atmospheric air, the carbonic acid, notwithstanding -its superior specific gravity, rapidly escapes, and does so without -the exchange of an equivalent portion of atmospheric air; the bladder -is consequently forcibly depressed into the receiver. If the converse -of this experiment be tried, and the receiver, containing atmospheric -air, be tied over with a piece of bladder or thin leather, and then be -immersed in carbonic acid, this gas will so abundantly penetrate the -membrane and enter the receiver as to endanger its bursting. - -879. Dr. Stevens had repeated opportunities of verifying these facts, -during a stay which he made at Saratoga, in the United States, the -springs at which place liberate a large quantity of carbonic acid. -In the high rocks it often collects in considerable quantity and -purity, and experiments on dogs and rabbits are often made for the -entertainment of strangers, as at the Grotto del Cano, near Naples. -This rock stands by itself in a low valley, through which there run two -currents of water, the one fresh and superficial, the other beneath -and charged with salts and carbonic acid. A current of this water rises -to some height in a cavity of the high rock, which appears to have been -formed by a deposition of earthy salts from the water. It has a conical -figure, the base of which is below the surface of the ground, and is -about nine feet in diameter. It rises about five feet from the ground, -where it is truncated, and presents an aperture a foot in diameter. The -water rises in general only about two feet above the ground, and in the -three feet above the surface of the water the liberated carbonic acid -collects. By luting a large funnel over the aperture, carbonic acid may -be collected at the mouth of the funnel in indefinite quantities, of -which Dr. Stevens availed himself to multiply and vary his experiments, -the result of which appears to be the complete establishment of the -fact that there exists a powerful attraction between carbonic acid and -oxygen. - -880. The application of this fact to the explanation of the phenomena -of respiration is highly interesting. By virtue of this mutual -attraction, two currents are established, which flow in opposite -directions, through the membranous matter of the air-vesicles of the -lungs and the pulmonary blood-vessels spread out upon their surface; -the oxygen of the air flows to the blood attracted by its carbonic -acid, and the carbonic acid of the blood flows to the air attracted by -its oxygen. According to Dr. Stevens, the moment the blood parts with -its carbonic acid it loses its dark colour, and becomes of a bright -vermilion colour, for the following reason: all acids impart a dark -colour to the blood. With respect to most acids, this colour remains, -although the added acid be afterwards saturated. Carbonic acid forms an -exception, for on the removal of this aërial acid the blood resumes its -bright and arterial colour. Alkalies, like acids, darken the colour of -the blood, but salts produce a bright and vermilion colour when added -to the colouring matter of the blood. When the blood loses its carbonic -acid, the salts contained in the blood produce upon its colouring -matter the vermilion tint natural to the combination when the influence -of the salts is not counteracted by the presence of a redundant acid. -At the moment the venous blood gives up its carbonic acid it receives -in exchange a portion of the inspired air, which is chiefly at the -expense of the oxygen. It retains somewhat more oxygen than it yields -back in the shape of carbonic acid. The reddened and oxygenated blood, -having returned to the heart, is diffused over the system, where -it parts with its oxygen and combines with carbon, forming by the -union carbonic acid; the necessary result of this combination is the -generation of animal heat in the exact proportion to the quantity of -the carbonic acid which is produced. The venous blood, which receives -the carbonic acid as it is formed in the system, is darkened by its -presence, which counteracts the effects of the salts of the blood upon -its colouring matter. - -881. An account has been given (439) of the experiments, which prove -that the lungs also constantly exhale a quantity of azote. - -882. It has been further shown (469) that, together with the carbonic -acid, which passes off in the inspired air, there is always present a -quantity of aqueous vapour. This aqueous vapour is not visible at the -ordinary temperature of the air in its ordinary hygrometric state, -because the water is then dissolved in the air, and is carried off -in the form of invisible vapour; but it becomes abundantly manifest -at a low temperature, or when the air is loaded with moisture. By -the removal of this aqueous vapour, the lungs assist the skin in the -depuration of the blood. The water transpired by the lungs, like that -perspired through the skin, is separated from the blood by a true -and proper secretion constituting the pulmonary transudation. It is -commonly estimated that the lungs exhale about one-third as much as -the skin, or fifteen ounces daily. Dalton estimates it at twenty-four -ounces. - -883. These estimates of the quantity of fluid lost by cutaneous -and pulmonary transpiration relate to the quantities lost at the -ordinary external temperatures in which the human body is placed. The -quantity lost when the body is exposed to an elevated temperature is -prodigiously increased. It did not occur to the physiologists, whose -experiments have been detailed (492, _et seq._), to ascertain this -by causing themselves to be accurately weighed immediately before -they entered their heated chamber and immediately after they left it. -Having heard that the loss daily sustained by the workmen employed in -gas-works is very extraordinary, I endeavoured to ascertain the amount -of it with exactness. This I have been enabled to accomplish by the -assistance of Mr. Monro, the manager of the Phœnix Gas Works, and of -Mr. Cooper. The following are the experiments by which this has been -ascertained. - - -EXPERIMENT I.—November 18, 1836, at the Phœnix Gas Works, Bankside, -London. - -884. Eight of the workmen regularly employed at this establishment in -drawing and charging the retorts and in making up the fires, which -labour they perform twice every day, commonly for the space of one -hour, were accurately weighed in their clothes immediately before they -began and after they had finished their work. On this occasion they -continued at their work exactly three-quarters of an hour. In the -interval between the first and second weighing, the men were allowed -to partake of no solid or liquid, nor to part with either. The day was -bright and clear, with much wind. The men worked in the open air, the -temperature of which was 60° Farh. The barometer 29° 25´ to 29° 4´. - - Weight of the Men Weight of the Men Loss. - before they began after they had - their work. finished their work. - - cwt. qr. lbs. oz. cwt. qr. lbs. oz. lbs. oz. - Michael Griffiths 1 1 14 10 1 1 12 2 2 8 - John Kenny 1 0 26 10 1 0 24 1 2 9 - John Ives 1 0 14 2 1 0 11 8 2 10 - James Finnigan 1 1 10 6 1 1 7 0 3 6 - William Hummerson 1 0 24 4 1 0 20 8 3 12 - Timothy Frawley 1 1 8 10 1 1 4 12 3 14 - Patrick Nearey 1 1 14 10 1 1 10 8 4 2 - Bryan Glynon 1 1 0 4 1 0 24 1 4 3 - - -EXPERIMENT II.—Nov. 25, 1836. - -885. Day foggy, with scarcely any wind. Temperature of the air 39° -Farh., barometer 29° 8´. On this occasion the men continued at their -labour one hour and a quarter. - - Before. After. Loss. - - cwt. qr. lbs. oz. cwt. qr. lbs. oz. lbs. oz. - Patrick Murphy 1 1 0 0 1 0 27 2 0 14 - John Broderick 1 0 9 4 1 0 8 0 1 4 - Michael Macarthy 1 0 11 9 1 0 10 3 1 6 - Michael Griffiths 1 1 15 8 1 1 13 2 2 6 - James Finnigan 1 1 12 4 1 1 9 12 2 8 - Bryan Duffy 1 1 11 12 1 1 9 0 2 12 - John Didderick 1 1 11 5 1 1 8 8 2 13 - Charles Cahell 1 1 4 5 1 1 1 6 2 15 - -886. Charles Cahell, the man who on this occasion lost the most, was -weighed previously to the commencement of his work, with all his -clothes off, excepting his shirt, which was kept dry and put on him -again when weighed a second time at the end of his work. He was then -immediately put into a warm bath at 95° Farh., and kept there half an -hour: he complained of being weak and faint, and when reweighed had -gained half a pound. - - -EXPERIMENT III.—June 4, 1837. - -887. Day clear, with some wind. Temperature 60° 5´. - - Before. After. Loss. - - cwt. qr. lbs. oz. cwt. qr. lbs. oz. lbs. oz. - Robert Bowers 1 1 19 0 1 1 17 0 2 0 - William Mullins 1 1 3 0 1 1 1 0 2 0 - Charles Cahell 1 1 2 0 1 1 0 0 2 0 - John Kenny 1 0 22 2 1 0 19 8 2 10 - Bryan Glynon 1 0 27 0 1 0 24 4 2 12 - John Haley 1 1 4 0 1 1 1 4 2 12 - Benjamin Faulkner 1 1 15 14 1 1 13 0 2 14 - Michael Griffiths 1 1 8 8 1 1 5 8 3 0 - John Broderick 1 0 4 6 0 3 27 8 4 14 - John Didderick 1 1 6 12 1 1 1 10 5 2 - -888. The two last men worked in a very hot place for one hour and ten -minutes; all the rest worked about one hour. Michael Griffiths, as -soon as he had finished his work, was put into a bath at 98°, where he -remained half an hour. He was reweighed on coming out of the bath, and -had lost 8 oz. - -889. From these observations it appears that, towards the end of -November, when the temperature of the external air was 39°, and the day -was foggy and without wind, the greatest loss did not amount to 3 lbs. -(2 lbs. 15 oz.), the least loss was 14 oz., and the average loss was 2 -lbs. 3 oz. - -890. In the middle of the same month, when the temperature of the air -was 60°, and the day was clear with much wind, the greatest loss was 4 -lbs. 3 oz., the least loss was 2 lbs. 8 oz., and the average loss was 3 -lbs. 6 oz. - -891. In June, when the temperature of the external air was 60°, and the -day exceedingly bright and clear, without much wind, the greatest loss -was 5 lbs. 2 oz., the next greatest loss was 4 lbs. 14 oz., the least -loss was 2 lbs., and the average loss was 2 lbs. 8 oz. - -892. The same individuals lose very different quantities at different -times. Thus, James Finnigan in the first experiment lost 3 lbs. 6 oz., -in the second 2 lbs. 8oz. Michael Griffiths in the first experiment -lost 2 lbs. 8oz., in the second 2 lbs. 6 oz., and in the third 3 lbs.; -while John Kenny in the first experiment lost 2 lbs. 9 oz., and in the -third experiment, which was the second to which he was subjected, he -lost very nearly the same, namely, 2 lbs. 10 oz. On the other hand, -Bryan Glynon in the first experiment lost 4 lbs. 3 oz., and in the -third experiment, which was the second to which he was subjected, he -lost no more than 2 lbs. 12 oz. - -893. In one case, when a man who had lost 2 lbs. 15 oz., the greatest -quantity lost by any of the men examined during that day, was put into -a hot bath at 95°, and reweighed on coming out of the bath, where he -had remained exactly half an hour, it was found that he had gained half -a pound. On the other hand, when a man who had lost 3 lbs. was put -into a hot bath at 98°, and kept there for half an hour and reweighed, -it was found that he had lost exactly half a pound. - -894. It was our intention to have pursued these experiments, with the -view of ascertaining the influence of the hygrometrical state of the -air on transpiration, as well as the absorbing power of the skin, under -circumstances so favourable to the activity of that power, but the -investigation has been unavoidably postponed. - -895. The results of these observations are as interesting in relation -to absorption as to transpiration. Thus, James Finnigan, on the 18th of -November, weighed, - - cwt. qr. lbs. oz. - - before the experiment 1 1 10 6 - after the experiment 1 1 7 0 - having lost 0 0 3 6 - -On the 25th of November he weighed 1 cwt. 1 qr. 12 lbs. 4 oz., having -gained in the interval 1 lb. 14 oz. - -Michael Griffiths, on the 18th of November, - - cwt. qr. lbs. oz. - - before the experiment, weighed 1 1 14 10 - after the experiment 1 1 12 2 - having lost 0 0 2 8 - -On the 25th of November, before the experiment, he weighed 1 cwt. 1 qr. -15 lbs. 8oz., having gained 14 oz.; but on the 3rd of June he weighed -1 cwt. 1 qr. 8 lbs. 8 oz., having lost between the 18th of November and -the 3rd of June, 6 lbs. 2 oz. - -896. John Kenny, on the 18th of November, - - cwt. lbs. oz. - before the experiment, weighed 1 26 10 - after the experiment 1 24 1 - having lost 0 2 9 - -On June the 3rd he weighed 1 cwt. 22 lbs. 2oz., having gained in the -interval 4 lbs. 8 oz. - -897. Bryan Glynon, November 18th, - - cwt. qr. lbs. oz. - before the experiment, weighed 1 1 0 4 - after the experiment 1 0 24 1 - having lost 0 0 4 3 - -On the 3rd of June he weighed 1 cwt. 27 lbs., having lost 1 lb. 4 oz. - -898. Thus, in the course of their ordinary occupation, these men are in -the habit of losing from 2 lbs. to 5 lbs. and upwards twice a-day; yet, -when weighed at distant intervals, it is found that some have actually -gained in weight and others have lost only a few pounds; it follows -that the activity of the daily absorption must be proportionate to that -of the daily transpiration. - -899. According to the prevalent opinion, the liver is the cause of -a large proportion of the maladies which afflict and destroy human -life. It certainly exercises an important influence over health and -disease, the true reason of which is but little understood by those who -attribute most to its agency. - -900. The liver is an organ of digestion and an organ of excretion. - -It is an organ of digestion in a two-fold mode: - -1. By the secretion of a peculiar fluid, through the direct action of -which chyme is converted into chyle. The several phenomena attending -this operation have been fully described (668 _et seq._). - -2. By subjecting alimentary matters which have been partly acted on by -the stomach and intestines to a second digestion. - -901. It has been shown (666) that the veins which return the blood from -the digestive organs, the stomach, the intestines, and the mesentery, -together with the veins of the spleen, the omentum and the pancreas, -instead of pursuing a direct course to the right side of the heart in -order to transmit their contents by the shortest route to the lungs, as -is the case with all the other veins of the body, unite together and -form a large trunk termed the vena portæ, which enters the liver and -ramifies through it in the manner of an artery. It has been further -shown (666) that the bile is secreted from the venous blood contained -in this vessel by its capillary branches spread out on the walls of -the biliary ducts, the only known instance in the human body in which -a secretion is formed from venous blood by venous capillaries; that -the trunk of this vein, unlike that of any other, is encompassed with -organic nerves, which accompany its subdivisions, and are spread out -upon its capillary branches just as an organic nerve is spent upon -an artery, and that thus, as this vessel performs the function of an -artery, it has the structure and distribution of an artery. - -902. The veins which unite to form the vena portæ take up, by their -capillary branches, certain portions of the contents of their -respective organs, and bear those contents directly into the venous -current. The capillary veins of the stomach take up certain parts of -the contents of the stomach, it would appear the fluid substances -received with the aliment more especially; the capillary veins of the -duodenum take up certain portions of the contents of the duodenum, and -so on of the capillary veins of the spleen, intestines, and all the -organs whose veins combine to form the vena portæ. Further, branches -of the absorbent vessels of these organs have been distinctly traced -opening directly into the veins in their immediate neighbourhood. -Certain products of digestion must, then, be constantly poured, both -by the capillary veins and by the absorbent vessels of the digestive -organs, into the blood of the vena portæ. - -903. Accordingly, on the examination of animals soon after a meal, -streaks of a substance like chyle are often observed in the blood of -the vena portæ. It is further established by numerous experiments, -that if alcohol, gamboge, indigo, and other odoriferous and colouring -matters, are mixed with the food, their presence is manifest in the -blood of the digestive organs, and more especially in the blood of the -mesenteric veins and in that of the vena portæ, while no trace of these -substances is ever found in the lacteals. - -904. The lacteals, it has been shown (835. 1.), are special organs -appropriated to the performance of a specific function, that of -absorbing chyle. To fit them for this office, they are endowed with an -elective power, by virtue of which they select, from the alimentary -mass, that portion of it only which is converted into chyle; in -a natural and healthy state they would appear to be incapable of -absorbing any other substance excepting pure chyle. But in the -digestive organs there is always present much nutritive matter not -yet converted into proper chyle, and with this matter there are mixed -foreign substances not strictly alimentary. These unassimilated matters -and foreign substances, absorbed by the capillary veins or by the -absorbent vessels, or by both, are conveyed directly into the vena -portæ, by which vessel they are transmitted to the liver, where they -undergo a true and proper digestion. After undergoing this digestion -in the liver, they are sent by a short course to the heart, and thence -to the lungs, where they are assimilated into, or at least commingled -with, arterial blood, and, with arterial blood, are transmitted to the -system. The substances subjected to this hepatic digestion, which is -as real as that effected in the stomach and duodenum, do not appear -to enter the lacteals at all; they have therefore a shorter course -to traverse, and probably a proportionately less elaborate process -to undergo, before their transmission to the lungs and their final -entrance into the arterial system. - -905. What the particular substances are for which this slighter -digestive process suffices is not known with certainty. There is, -however, reason to suppose that they consist chiefly of liquids, while -there is direct evidence that vinous and spirituous liquids enter -the system through this shorter course; since these fluids are often -abundantly manifest in the blood of the vena portæ, when not the -slightest trace of them can be detected in the lacteal vessels. - -906. According to this view, the liver is a second digestive -apparatus, completing what the first commences, or effecting what -that is incapable of accomplishing; and this view assigns the reason -why certain fluids taken into the stomach sometimes appear in the -secretions and excretions with such astonishing rapidity; why the liver -so constantly becomes diseased when highly stimulating substances, not -properly alimentary, are mixed with the food, and more especially when -ardent spirits or the stronger wines are largely and habitually taken; -why the sympathy is so intimate and intense between the stomach and -the liver and the liver and the stomach, both in health and disease; -why in the ascending animal series the liver so soon appears after -the stomach, and why the magnitude of the organ and the elaborateness -of its structure progressively increase with the extension of the -digestive apparatus and the corresponding complexity of the general -organization. - -907. The second function performed by the liver is that of excretion. -The excrementitious matter eliminated from the blood by the liver is -contained in its peculiar secretion, the bile. The bile consists of -two portions, an assimilative part which combines chemically with the -chyle, purifying and exalting its nature; and an excrementitious part -which combines with the residue of the aliment. - -908. The excrementitious part of the bile contains a large proportion -of carbon and hydrogen. Carbon and hydrogen abound in venous blood; -venous blood in large quantity is sent to the liver to afford the -materials for the secretion of bile; consequently, the more copious -the secretion of bile the greater the quantity of carbon and hydrogen -abstracted from venous blood. It follows that, by this elimination of -carbon and hydrogen from the blood, the liver is auxiliary, as an -organ of excretion, to the skin and the lungs. - -909. But it is well worthy of remark, that although the liver at all -times assists the skin and the lungs in carrying on the process of -excretion, it does this most especially under circumstances which -necessarily enfeeble the action of the cutaneous and pulmonary organs. - -910. Less carbon is expelled from the lungs in summer than in winter; -at a high than at a low temperature; consequently by a long-continued -exposure to intense heat, as in the hot months of summer, and still -more by a continual residence in a warm climate, an accumulation of -carbon in the blood is favoured. A part of this excess is removed by -the increased exhalation from the skin. The skin, however, is the -chief outlet, not for carbon, but for hydrogen; and accordingly by the -increased perspiration hydrogen is largely removed. Hydrogen and carbon -compose fat. The deposition of fat, could it go on to the requisite -extent, would afford an adequate consumption for the superabundant -carbon; but the formation of fat is prevented by the dissipation of the -hydrogen. Under such circumstances, when the lungs cannot carry off the -requisite quantity of carbon, nor the adipose tissue compensate for its -diminished activity by the deposition of fat, the liver, taking on an -increased action, secretes an extraordinary quantity of bile. In this -manner the superfluous carbon, instead of being removed in the ordinary -mode, by the pulmonary artery through the lungs, under the form of -carbonic acid gas, is excreted by the vena portæ, through the liver, -under the form of bile, while the superabundant hydrogen is removed by -the increased quantity of perspiration; and thus the accumulation of -these inflammable matters in the system is effectually prevented. - -911. By the deposition of fat in the adipose tissue material assistance -is afforded to the excretory action of the skin, the lungs, and -the liver. Fat is composed essentially of carbon and hydrogen; it -contains no nitrogen and very little oxygen. It is deposited whenever -an excessive quantity of nutritive matter is poured into the blood, -and especially when at the same time the different secretions and -excretions ordinarily formed from the blood are diminished. The primary -object of this deposition is to relieve the circulation of a load which -would embarrass and ultimately stop the actions of life. It serves, -however, a secondary purpose, that of forming a storehouse of nutritive -matter, duly prepared for supplying the wants of the system, in case -the body should be placed under circumstances in which the digestive -organs can no longer receive food or no longer convert it into chyle. - -912. Thus hybernating animals, which pass many months without taking -food, accumulate a store of fat before they fall into the state of -torpor. Marmots and dormice subsist on this store during the winter, -and hence, when spring awakens them from their torpor, they are always -in a state of extreme emaciation. Birds and other animals which live on -food procured with difficulty in the winter, become unusually fat in -the autumn. - -913. During fever and other acute diseases, when little food is -received, and still less converted into chyle, the extreme emaciation -which the body undergoes is owing partly to the disappearance of the -fat, which is taken up by the absorbents and carried into the blood, in -order to compensate for the deficiency of nutrient matter supplied by -the digestive organs. - -914. The chief depositories of the fat are those intersticial spaces of -the body in which a certain quantity of soft but tenaceous substance is -required to obviate pressure or to preserve symmetry. A large quantity -is also placed immediately beneath the skin; in the interstices of -muscles; along the course of blood-vessels and nerves; in the omentum, -where it is spread like a covering over the viscera of the abdomen -(fig. CLXX. 7); in the mesentery and around the kidneys. - -915. Fat is a bad conductor of heat; consequently the layer which is -spread over the external surface immediately beneath the skin, and -that which is collected in the interior of the omentum, must be useful -in preserving the heat of the body. Fat persons bear cold better than -lean persons. Animals which inhabit the northern climates, and the -fishes of the frozen seas, are enveloped in prodigious quantities of -fat. Where the accumulation of this substance would produce deformity -or interfere with function, as about the joints, in the eyelids, within -the skull, not a particle is ever deposited. About the joints it would -impede motion; in the eyelids it would render the face hideous and -obstruct vision; and within the skull, a cavity completely filled -with the brain, an organ impatient of the slightest pressure, had a -substance been placed, the quantity of which is liable to be suddenly -trebled or quadrupled, changes in the system which now produce no -inconvenience would have been fatal. Thus, while provision is made at -once to exonerate the system from too great a load of nourishment, and -to lay up the superfluous matter, as in a magazine, to be ready for -future use, the most extreme care is taken to deposit the store in safe -and convenient situations. - -916. The excretory organs and processes, hitherto considered, have for -their object the removal from the blood of its superfluous carbon and -hydrogen; the element peculiar to the animal body, azote, is eliminated -by the kidneys, glandular organs which possess a highly complex -structure. - -917. But besides the removal of the superfluous azote, the fluid -secreted by the kidneys would appear to be a general outlet for -whatever is not required in the system, and for the removal of which -no specific apparatus is provided. Chemical analysis shows that, in -different states of the system, the following substances are contained -in this fluid:—water, free phosphoric acid, phosphate of lime, -phosphate of magnesia, floric acid, uric acid, benzoic acid, lactic -acid, urea, gelatin, albumen, lactate of ammonia, sulphate of potash, -sulphate of soda, fluate of lime, muriate of soda, phosphate of soda, -phosphate of ammonia, sulphur, and silex. - -918. This catalogue itself suggests the idea that when any matter -employed in carrying on the functions is in excess, or when it has -become decayed, or is decomposed and is not eliminated by any other -excretory process, it is taken up by the absorbents, poured into the -veins, and so conveyed in the course of the circulation to the kidneys, -by which organs it is separated from the blood, and thence by an -appropriate apparatus carried out of the system. - -919. The specific matter secreted by the kidneys is that termed urea; -a substance of a resinous nature, highly animalized. One character by -which the animal is distinguished from the plant is its locomotion. -The organ by which the animal is rendered capable of performing the -function of locomotion is muscle or flesh. The basis of muscle is -fibrin, and the basis of fibrin azote. There must be in the animal -body an abundant supply of fibrin, and consequently a proportionate -abundance of azote. Azote is introduced into the system partly by the -food and partly by the lungs. That there may be a sufficiency for all -occasions, more is introduced than is necessary on ordinary occasions, -and a special outlet is established for the excess through the kidneys. - -920. Organs appropriated to the removal of substances from the blood, -capable of becoming deleterious by their accumulation, generally in -a state of health perform their office so perfectly that the matters -which it is their part to excrete are eliminated almost as quickly -as they enter the blood, so that they are seldom present in the -circulating fluid in sufficient quantity to be detected by the most -delicate chemical tests. But by the removal of the excretory organ, or -by the suppression of its function, the excretory matter accumulates -in the blood, and is then readily detected. A decisive experiment -disclosed that this is the case with regard to urea. The kidneys were -removed from a living animal. The operation did not appear to be -productive of material injury for some time; but at length symptoms -denoting the presence of a poison in the blood arose, and the animal -died. The blood was carefully examined after death. It was found to -contain a much larger quantity than ordinary of the peculiar animal -substance which enters into the composition of the serosity of the -blood (225). On subjecting this substance to the action of various -re-agents, and also on reducing it to its ultimate elements, it was -found to resemble urea; to be, in fact, nearly identical with urea as -contained in the urine. From this experiment it became manifest that -the source of the urea is the serosity of the blood. It is probable -that the chief office of the kidney is to separate the urea from the -other ingredients of the blood, and to convey it to the organs which -are destined to carry it out of the body. - -921. It is estimated that about a thousand ounces of blood pass through -the kidneys in the space of an hour; itself a sufficient indication -of the importance of the excretion performed by this organ, and an -adequate source of the matter actually excreted, although, under -ordinary circumstances, distributed through the circulating mass in -quantities so minute as to be almost inappreciable. - -922. From the power of absorption possessed by the veins of the stomach -and intestines, from the connexion proved to be established between -the venous and absorbent systems, and from the discovery of Lippi, that -several absorbent branches in the abdomen terminate directly in the -pelvis of the kidney, that is now an established fact which was long -a conjecture, that there exists a short route from the stomach to the -kidneys, so that the extreme rapidity with which certain substances -mixed with the aliment appear in the fluid secreted by the kidneys is -no longer a matter of wonder. - -923. Out of the body urea putrifies with great rapidity. When retained -in the system by the extirpation of the kidney, or by placing a -ligature around the ureter, such is the septic tendency communicated to -the blood that signs of putrescency become manifest even during life, -and after death all the soft parts of the body are reduced to a state -of putrefaction with extreme rapidity. The suppression of the secretion -in the human body, or the undue retention of the matter secreted, -induces fever of a malignant kind, in which the symptoms that denote a -highly putrid taint in the system are rapidly developed. But for the -labour of the kidney, then, a substance would accumulate in the blood, -which would quickly lead to the decomposition of the body. - -924. It has been shown that the mucous membrane which lines the -alimentary canal is studded in its whole extent with glands, which -secrete from the blood a large quantity of fluid, These secretions go -on without interruption, whether food be taken or not, so that there -may be copious alvine evacuations though not a particle of food enter -the stomach; and the separation of the matter eliminated from the blood -by this extended membrane can no more be dispensed with than that by -the skin or the lungs. There is, too, a most intimate sympathy between -the secretion of the membrane that lines the internal surface of the -body and that carried on by its external covering; any disorder of -the one immediately and powerfully disturbs the natural course of the -other: hence the diarrhœa, so often produced by the application of -cold to the external skin, and the diseases of the skin, so constantly -connected with a disordered state of the mucous membrane of the -intestines. - -925. It is the special office of the large intestines to prepare for -its removal, and to carry out of the system the residue of the aliment, -together with the excrementitious portion of the bile. - -926. It was calculated by Haller, that the different excretory organs -remove from the system every twenty-four hours twenty pounds of matter. -Of this total loss sustained daily by the human body, it was estimated -that four pounds are removed by the skin, four pounds by the lungs, -four pounds by the kidneys, and eight pounds by the intestinal canal. -In this estimate, which is considered too large, especially that -by the intestinal canal, the quantity stated must be understood as -denoting the maximum of each secretion. - -927. Supposing the ingesta in twenty-four hours to be of food 6 pounds, -or 96 ounces, and of oxygen retained in the system 4 ounces, in all 100 -ounces, it is estimated that the egesta will be, in twenty-four hours, -by the skin, 34 ounces, by the lungs 17 ounces, by the intestines 6 -ounces, by the kidneys 40 ounces, and by various other excretions -3 ounces, in all, 100 ounces. These calculations must of course be -taken only as approximations to the truth, and as ascribing rather the -relative than the positive quantities of matter excreted. - -928. Whatever be the absolute quantity or the form of the excretions, -it is clear, from the preceding account, that there is constantly -removed from the system by the skin a large portion of hydrogen and -some carbon; by the lungs a large portion of carbon and some hydrogen; -by the liver a large portion of hydrogen and some carbon; by the -kidneys a large portion of azote; by the large intestines the residue -of the aliment; while, by the deposition of fat, the superabundant -nutriment withdrawn from the current of the circulation is laid up in -store in some safe part of the body. - -929. Most of the processes which have been described are mutually -compensating and vicarious. Besides the office which each habitually -performs, it is capable of having its action occasionally increased, -for the purpose of supplying the deficiency of one or more of its -fellows. If perspiration by the skin languish, transudation by the -lungs increases; if neither the skin nor the lungs be able to remove -the superfluous hydrogen and carbon, these inflammable substances are -carried out of the system by the liver in an augmented secretion of -bile. If the action of the liver be diminished, that of the kidney is -increased; and if the secretion of urine be suppressed, the secretion -of bile is augmented. When the absorbents are oppressed by the quantity -of fluid poured into the stomach, or when the system is at the point -of saturation, and no absorption can go on, the veins take up the -superfluous liquids, pour them into the circulating current, and bear -them to the kidneys, by which organs they are rapidly separated from -the blood, and carried out of the body. The weakness of one organ is -compensated by the strength of another; the diminished activity of one -process is equalized by the increased energy of some other to which it -is allied in nature and linked by sympathy; and thus the evils which -would result from the partial and temporary failure of an important -function are obviated by some vicarious labour, until the enfeebled -organ has recovered its tone, and the natural balance of the functions -is restored. - -930. The condition acquired by the elementary particles of organized -bodies, from their long continuance in the system, which induces the -necessity for their excretion, is not known. The chemical elements -of the excretions are the very same as those which constitute the -organized textures and the nourishment by which they are sustained. -Carbon is the basis of the organized body; yet all living bodies, -without exception, excrete carbon. Oxygen, hydrogen, and azote, also, -without which life cannot be maintained, if retained in the system -beyond a given time, are incompatible with the continuance of life. -During the chemical changes which these elementary particles undergo, -in the course of the vital processes, they appear to enter into some -combination, which is no longer compatible with the peculiar mode in -which they are disposed in organized and living structures. And one -such change, of a very remarkable nature, has been observed, which, -it is conceived, has a considerable share in rendering their constant -expulsion and renovation indispensable. - -931. Out of the condition of life the component elements of organized -bodies readily combine so as to form crystals; the peculiar -combinations by which they form the constituent textures of organic -structures are never crystalline. No crystal is ever seen in the seat -of a living and growing vegetable cellule; no crystal is ever found -as a constituent part of animal membrane. Whenever a crystal occurs -in an organized body it is always the result either of disease or of -some artificial process, or else it is an excretion separated from the -nourishing fluid and the useful textures. Every one of these textures -contains, even in its minutest parts, saline and earthy, as well -as vegetable or animal, matter. Why do not these saline and earthy -particles as readily combine to form crystals in the organic as they do -in the inorganic body? They never do. In the organic body these saline -and earthy particles are always so arranged that they are diffused -through the membranous fibres or cells, never concentrated in crystals. - -932. On the other hand, the elements containing the peculiar matters of -excretion are generally in such a state of combination as readily to -assume the crystalline form, either alone or in the simplest further -combinations of which they are susceptible. It seems probable that this -circumstance may be, at least in part, the cause which necessitates -their expulsion, and it is certain that some such general principle -must determine the incompatibility of the matters of excretion with the -life of the structures - -933. The ultimate object of the processes included in the function of -excretion is to maintain the nutritive fluid in a certain chemical -condition. Into the combination of the blood there must enter certain -constituents, and these must be in certain relative proportions, and -in no others. If the salts be diminished or in excess, if the fibrin, -or the red particles, or the serum be abundant or defective beyond a -certain degree, either the necessary chemical elements are not present, -or not present in the form necessary to their entering into the -requisite combinations; the result is, that a proper nutritive fluid -is not formed, and consequently due nourishment is not afforded to the -textures nor due stimulus to the moving powers; there is either too -much nutriment and stimulus or too little; in the one case the machine -is exhausted and worn out, and in the other it is clogged and stopped. - -934. The capillary arteries of the skin, and of all the other tissues -into the composition of which gelatin enters as a constituent, -necessarily pour carbon into the capillary veins at the moment they -convert albumen into gelatin (539). The veins, receiving in their -course more and more carbon from the arteries, at length become loaded -with this element, and in order to get rid of the excess they bear -it to the lungs, where it is expelled by the act of expiration under -the form of carbonic acid gas. On the other hand the chyle, gradually -becoming firmer and more condensed by the series of changes which it -undergoes from its first formation in the duodenum to its admixture -with the lymph in the receptacle of the chyle, and with the blood -in the subclavian vein, is hurried to the heart and thence to the -lungs, where it gives off a large portion of its watery particles, -also by the act of expiration, under the form of aqueous vapour. This -excretion of its watery particles is a necessary part of the process of -completion by which the weak albumen of the chyle is converted into the -strong albumen of the blood (703. 3). How completely analogous then is -this excretory process in the plant and in the animal! How precisely -the same is the action of the leaf and of the lung! The leaf dissipates -the superfluous water of the crude sap, concentrates its organic -principles, and brings it into the chemical condition which constitutes -the proper juice of the plant; the lung removes the superfluous water -of the chyle, concentrates its organic principles, and completely -assimilates its chemical nature into that of the blood. - -935. It is the same with every other process of excretion; its uniform -result is to alter the chemical composition of the nutritive fluid, to -restore it to a state of concentration and purity. Excretion then is -appropriately termed a depurating process. - -936. The effect of the suppression of excretion, when the suppression -is complete, is appalling. Stop the respiration, that is, suspend -the depurating action of the lungs, carbon accumulates in the venous -blood; carbon mixes with the arterial blood; in half a minute the -blood flowing in the arteries is evidently darkened; in three-quarters -of a minute it is of a dusky hue; in a minute and a half it is quite -black; every particle of arterial blood has now disappeared, and the -whole mass is become venous. With the first appearance of the dusky hue -great disturbance is produced in the system; the instant it becomes -dark sensibility is abolished; in a few minutes after it is black the -power of the heart is so enfeebled that it can no longer carry on the -circulation, and in a few minutes more its action wholly ceases, and -can never again be excited. The brain feels the poison first, and is -first killed; but the heart cannot long resist the fatal influence. - -937. Stop the excretion of the kidney by the extirpation of the organ, -or the suppression of its secretion, urea accumulates in the blood; the -poison, after a short time, begins to work; fever is excited, and then, -with fearful rapidity, fever is followed by coma, and coma by death. - -938. Stop the secretion of bile, a poison accumulates in the blood as -potent, producing insensibility and death as rapidly, as that generated -by the suppression of the depurating action of the kidneys. - -939. Only obstruct the secretion of bile, merely prevent its due -elimination from the blood, just in proportion to its suppression does -the system suffer from languor, lassitude, and inaptitude for every -muscular and mental exertion. - -940. How do the internal organs suffer when the excretion of the skin -is deficient, and how numberless and hideous are the diseases of the -skin when the depurating process of the alimentary canal is suspended! - -941. When, on the contrary, all these excretions are well and duly -performed, how regular and tranquil, yet how full and strong the flow -of the circulating current; how rich the stream poured by it into every -organ; how healthfully exciting its influence on them all; how gentle, -how efficient, every organic action; how complete the absence of all -note or sensible intimation that any such action is going on, yet how -delicious the consciousness produced by its soundness and vigour; how -acute the sense, how bounding the motion, how quick the percipience; -how the pure blood mantles in the cheek and diffuses its sparkling -colour over all the transparent complexion; how the jocund spirits -laugh from the eyes; how the intellectual and sympathizing mind beams -forth from them with a higher and holier happiness! How wonderfully -beautiful is such a human body, and how magnificently endowed in its -capacity to give and to receive enjoyment! - -942. There are two adjustments, with regard to the excretions, carried -on by organized bodies, which can never be contemplated with sufficient -admiration. It has been fully shown (464 _et seq._) that the relation -established between the two great classes of organized beings is such -that the excrementitious matter of the plant is nutritious to the -animal, and the excrementitious matter of the animal is nutritious to -the plant; and, consequently, that the two orders of living beings -maintain the world, which is given them as their inheritance, in a -state of perpetual adaptation for the life and health of each other; -the animal receiving healthy stimulation from that which is poisonous -to the plant, and the plant being nourished by particles which the -animal throws off as exhausted and useless. And this relation naturally -suggests that so beautifully described by Milton:— - - Flow’rs and their fruit, - Man’s nourishment, by gradual scale sublimed - To vital spirits aspire, to animal, - To intellectual; give both life and sense, - Fancy and understanding; whence the soul - Reason receives. - -943. Secondly, the particles thrown off by organized bodies are -rendered, in the very act of their dissipation, subservient to purposes -of utility and pleasure. How these poisonous elements are converted -into the pabulum of life and health has been shown. To a being with the -senses and faculties of man, how loathsome might these particles have -been rendered during the period of their transition from one organized -kingdom to the other! And if disagreeable at all, how constantly forced -upon his sense, wherever he might be, during every moment of his -waking hours, must these objects of disgust have been! But how does -the matter actually stand? The excretions of the plant are the very -particles that, poured - - “Into the blissful field through groves of myrrh, - And flow’ring odours, cassia, nard, and balm,” - -create “a wilderness of sweets.” It is as these exhalations are passing -off from the economy to which, if retained, they would be noxious -(851), that they become - - “Exhalations of all sweets - That float o’er vale and upland;” - -and which refresh and delight even more than the forms and colours of -the “aery leaf” or “the bright consummate flower.” - -944. And the human body, when the functions of its economy are sound -and vigorous, is fresh and fragrant as the flower (862); and by that -intellectual faculty by which man is capable of associating his -conception of beauty and delight with whatever object has been the -source of exquisite gratification, the fragrance of the flower is but -suggestive of what, to him, is inexpressibly sweeter and dearer. - - “As new waked from soundest sleep, - Soft on the flow’ry herb I found me laid - In balmy sweat, which with his beams the sun - Soon dry’d—— - By quick instinctive motion up I sprung, - ——— And upright - Stood on my feet.—— - ——— All things smiled - With fragrance, and with joy my heart o’erflow’d. - Myself I then perused, and limb by limb - Survey’d, and sometimes went, and sometimes ran. - With supple joints, as lively vigour led.” MILTON. - - ——Fresh lily, - ’Tis her breathing that - Perfumes her chamber thus. SHAKSPEARE. - - —— The very air - With her sweet presence is impregnate richly, - As in a mead that’s fresh with youngest green - Some fragrant shrub exhales—— - Ambrosial odours—— - Charming present sense, - And sure of memory;—so her person bears - A natural balm—distilling incense. - “Death of Marlowe,” by R. H. HORNE. - - - - -CHAPTER XIV. - -OF NUTRITION. - - Composition of the blood—Liquor sanguinis—Recent account of the - structure of the red particles—Formation of the red particles in - the incubated egg—Primary motion of the blood—Vivifying influence - of the red particles—Influence of arterial and venous blood on - animal and organic life—Formation of human blood—Course of the new - constituents of the blood to the lungs—Space of time required for the - complete conversion of chyle into blood after its first transmission - through the lungs—Distribution of blood to the capillaries when - duly concentrated and purified—Changes wrought upon the blood while - it is traversing the capillaries—Evidence of an interchange of - particles between the blood and the tissues—Phenomena attending the - interchange—Nutrition, what, and how distinguished from digestion—How - the constituents of the blood escape from the circulation—Designation - of the general power to which vital phenomena are referrible—Conjoint - influence of the capillaries and absorbents in building up - structure—Influence of the organic nerves on the process—Physical - agent by which the organic nerves operate—Conclusion. - - -945. The object of the greater part of the processes hitherto described -is to form the nutritive fluid, and to bring it to the requisite state -of purity and strength. Recent researches into the composition of the -nutritive fluid confirm the general correctness of the account already -given of it, (211 _et seq._). - -946. When examined as it is flowing in the finest vessels of a -transparent part of the body, or immediately after it is abstracted -from the trunk of a vein or artery, before coagulation (218) takes -place, the blood is seen to consist of a colourless fluid, through -which is diffused a countless number of minute solid particles of a red -colour. The colourless fluid is called the liquor sanguinis, and the -solid particles the blood corpuscles or the red particles. - -947. By the process of coagulation, the phenomena of which have been -fully described (219 _et seq._), the blood spontaneously separates into -a clear fluid of a yellow colour called serum or blood-water, and into -a solid mass termed the clot or the crassamentum. The serum, which must -be carefully distinguished from the liquor sanguinis, is the fluid -formed from the blood by coagulation; the liquor sanguinis is the fluid -part of the blood which exists before coagulation. - -948. The liquor sanguinis contains in solution a large quantity of -animal matter, fibrin (228), which separates spontaneously in a solid -form on coagulation; the serum also contains a quantity of animal -matter in solution, albumen (224), which does not separate in a -solid form spontaneously, but only on the application of heat, acids, -alcohol, &c. (224). The animal matter, the fibrin, which separates -spontaneously from the liquor sanguinis in a solid form, constitutes -one part of the clot, and the other part of it consists of the red -particles which floated in the liquor sanguinis. - -949. Thus, by coagulation, the liquor sanguinis separates into a -portion which remains fluid, the serum; and into a portion which -becomes solid, the fibrin; while the fibrin, as it is passing from -the fluid to the solid state, entangles the red particles, and both -together form the clot; consequently the liquor sanguinis contains in -solution two kinds of solid matter, fibrin and albumen; while the serum -contains in solution only one kind of solid matter, albumen. - -950. The solution of fibrin in the liquor sanguinis, and its -spontaneous solidification during the process of coagulation, has been -shown by Professor Müller in the following mode. Having carefully -collected blood from the femoral artery of the frog, and also from the -heart laid bare and incised, and having brought a drop of this pure -blood under the microscope, and diluted it with serum, so that the -red particles were separated from each other by distant intervals, -he observed that there formed in those intervals a coagulation of -previously dissolved matter, by which the separated red particles were -connected together. By raising, with a needle, the coagulum occupying -the intervening spaces, this solid matter was obtained free from red -particles. The blood corpuscles of the frog are rendered, by a powerful -microscope, so large, that this operation may be performed with the -greatest distinctness. In consequence of the minuteness of the red -particles of human blood they pass, with the liquor sanguinis, through -filtering-paper; but those of the frog, being four times larger, are -kept back by the filter, while the liquor sanguinis percolates through -as a clear fluid, and then coagulates. This colourless coagulum is so -transparent that it is not even detected, after its formation, until -it is raised out of the fluid with a needle. It gradually thickens and -becomes white. It is the fibrin of the blood in its purest state. - -951. Professor Müller’s account of the structure of the red particles -differs in a material point from that given (231 _et seq._). He -agrees that they are rounded bodies (fig. CXII. 1), generally of -the same size, though some are seen larger than common, but never -double the mean diameter; that they are always quite flat (232); that -in a certain light they look as if they were hollowed out from the -edges to the centre (fig. CXII. 1); but, he adds, “that this spot -is a real depression, as some think, appears to me in the highest -degree improbable; for I have at last convinced myself that the blood -corpuscles of man and the mammalia contain a very small nucleus of -the diameter of the flat corpuscle. My observations prove beyond -doubt that the blood corpuscles of frogs and salamanders (fig. CXII. -4) contain a nucleus entirely different in its chemical relations -from the outer layer. With one of Frauenhofer’s microscopes I have -seen very distinctly, in the blood corpuscles of man an exceedingly -small, round, well-defined nucleus, yellower and brighter than the -transparent circumference. When the blood corpuscles are mixed, -under the microscope, with acetic acid, the shell is almost entirely -dissolved, and these small nuclei, which are seen with great difficulty -in human blood, remain, while those of the frog appear, very evidently -the nuclei observed earlier in the blood corpuscles. In man, the nuclei -within the corpuscles are so small, that the diameter does not exceed -the thickness of the flat corpuscles.” - -952. The enveloping capsule is stated to be soluble in water, while the -internal nucleus is insoluble; but the capsule is not soluble in serum; -the albumen and the salts contained in the serum probably rendering it -insoluble. The colouring matter of the capsule, which gives the red -colour to the blood, is called hæmatosin. Lecanu considers the capsular -substance as a combination of a specific colouring matter, which he -calls globulin, and of albumen; but Müller regards it as fibrin, -containing a quantity of iron. The latter physiologist states that -the opinion of Brande, that the amount of iron in hæmatosin is not -greater than in serum and other animal substances, has been refuted -by Berzelius and Engelhart. The iron is not an accidental ingredient -obtained from the food; for iron has been found in the blood of a -new-born animal that has never even sucked. According to Berzelius the -colouring matter of the blood contains a quantity of iron corresponding -to somewhat more than a half per cent. its weight of metallic iron, and -he thinks it most probable that the iron exists in the blood in the -metallic state, and not as an oxide. - -953. By carefully watching the development of the chick in the -incubated egg, the first formation of the red particles can be -distinctly seen. The blood in the new being, which is elaborated before -the existence of the vessels that are to contain it, is formed from -the substance of the germ or from that of the germinal membrane, and -is augmented by the blood of the egg, which is the substance of the -yolk. First, a number of granules are produced from the substance -of the yolk. These subsequently lose their granular appearance, and -become translucent. On the translucent ring is produced the nucleus -of the blood corpuscles. When completely formed, the blood corpuscles -of the bird, as of all the animals below the bird in the scale of -organization, are of an elliptical figure, and quite flat (fig. CXII. -4, 5); but when first produced they are rounded globules, not flat, and -they gradually assume their proper and permanent form; it is only on -the sixth day of incubation that they begin to be elliptical, by the -ninth day they are all elliptical (fig. CXII. 4, 5). - -954. The substance of the fluid yolk is thus changed into blood without -the action of any special organ; for, as yet, no organs such as liver, -spleen, or lungs, exist. When the formation of the blood has arrived -at a certain point, it begins to be in motion. The blood is seen to -be in motion before the heart can be observed to beat. The germinal -membrane arising out of the enlarged germinal disk soon exhibits a -thin upper layer (serous membrane) and a thicker under layer (mucous -membrane). There is also formed in the middle of the germinal membrane -around the appearing trace of the embryo a translucent space, the _area -pellucida_. The exterior of the germinal membrane remains opaque, and -this opaque portion becomes divided by a definite boundary into an -external and internal annular space in from sixteen to twenty hours. -This separation encloses one part of the opaque portion of the germinal -membrane, which surrounds the interior or translucent space of the -germinal membrane, and is termed _area vasculosa_, because the blood -and vessels form the inner half of this space. - -955. As far as the area vasculosa extends, a granular layer is -presented between the two layers of the germinal membrane, which soon -divides into numerous granular isolated particles with translucent -intervals, in which the blood collects, first in the form of a -yellowish, and then of a reddish fluid; first distinctly in the -periphery of the area vasculosa, from which it is seen to flow towards -the heart before the heart beats. - -956. The blood exerts its vivifying influence chiefly by the red -particles. If an animal be bled to fainting, and pure serum be injected -into its vessels, re-animation does not take place; but if the blood of -another animal of the same species be injected, the animal which was -apparently dead acquires new life at every stroke. - -957. The fibrin may be removed from the blood without injuring the -red particles. If the fibrin be abstracted, and a mixture of the -red particles and the serum be brought to a proper temperature, and -injected into the veins of an animal bled to fainting, re-animation is -effected. - -958. If the blood of an animal of another species be injected whose red -particles are of the same form, but of a different size, re-animation -is indeed effected, but the restoration is imperfect; the organic -functions are oppressed, and languish, and death takes place generally -within the sixth day. The same effects follow, if a mixture of serum -and red particles of the blood of a different species be injected. - -959. If blood with circular particles be injected into the vessels -of an animal whose blood corpuscles are elliptical, the most violent -effects are instantly produced; such blood acts upon the nervous system -like the strongest poisons; and death usually follows with extreme -rapidity after the injection of a very small quantity. Thus, if a few -drops of the blood of the sheep be injected into the vessels of the -bird, the bird is killed instantaneously. It is very remarkable, that -the blood of the mammalia should be thus fatal to the bird. The effect -cannot be dependent on any mechanical principle. The injection of a -fluid with particles, the diameter of which is greater than that of the -capillary blood-vessels would of course destroy life by stopping the -circulation; but the blood corpuscles of the mammalia are much smaller -than those of the bird; yet the pigeon is killed by a few drops of -mammiferous blood; and the blood of the fish is rapidly fatal to all -the mammalia as well as to birds. - -960. It is manifest, both from observation and experiment, that -arterial blood is far more necessary to the support of the animal than -of the organic life. When in asphyxia the communication of atmospheric -air with the lungs is suspended, the functions of the brain are -abolished; sensibility and voluntary motion are lost the moment venous -blood circulates in the arteries of the brain. It has been shown (476), -that if this state continue, the animal life is destroyed in a minute -and a half; but that the organic life is not extinguished for many -minutes, and sometimes not even for several hours. - -961. It sometimes happens that the communication between the pulmonary -artery and the aorta, and between the right and left auricle, which -naturally exist in the fœtus, is continued after birth. In persons -having this state of the circulation, called ceruleans, some portion -of venous blood is always mixed with arterial blood. In this case the -various processes of secretion and nutrition, the entire circle of -organic functions, are but little disturbed; while the animal functions -are deranged in a remarkable degree. The mind is weak and inactive, -and the muscular power is so feeble, that the least exertion produces -a sense of suffocation; and, if the muscular effort be continued, -occasions fainting, and even suspended animation. - -962. But while venous blood is in no case capable of supporting -sensation and voluntary motion, there are decided cases in which -secretion is effected, at least in part, from venous blood, as the bile -from the venous blood that circulates through the liver in man and all -the mammalia, and the urine which is formed from venous blood in some -of the lower orders of animals. - -963. The proper nutritive fluid of the human body is directly formed -from chyle, lymph, and venous blood; that is, partly from new matter -introduced into the system from the external world, and partly from -matter which has already formed a constituent part of the body. -The new matter, the white chyle, is prepared partly by the action -of the digestive fluids upon the food, and partly by the addition -to the digested food of highly animalized substances, endowed with -assimilative properties, by which the product is progressively -approximated to the chemical composition of the blood. The old matter -consists partly of the clear lymph, contained in the lymph vessels, -and derived from the interior of the organized parts, particles which -have already formed an integrant portion of the tissues and organs; and -partly of the dark venous blood, the residue of the proper nutritive -fluid, after the latter has yielded to the system the new matter -required by it, and has given off from the system its superfluous and -noxious particles. - -964. In the duodenum and jejunum the new matter, the chyle, contains -albumen; but it is without coagulable fibrin: it acquires fibrin in the -lymph vessels on its way to the veins. - -965. In the chyle globules appear; but the chyle corpuscles are white, -are without an external envelop, are comparatively few in number, are -somewhat more than half the size of the blood corpuscles, and, like the -nuclei of the latter, are insoluble in water. - -966. The fatty or oleaginous matter contained in the chyle is in a free -state, not intimately combined. - -967. The chyle is alkaline, but is much less alkaline than the blood; -and the iron contained in the chyle is much less intimately combined -than it is in the blood. - -968. Lymph contains in solution more animal matter than chyle, and the -white globules are more abundant in lymph. But though lymph contain -in solution more albumen and fibrin than chyle, it is not so richly -loaded with these substances as blood. Still, however, the solution of -albumen and fibrin in lymph approximates lymph so closely to the blood, -that the lymph very much resembles the clear liquor sanguinis of which -the blood consists when the red particles are abstracted from it. The -colourless liquor sanguinis is the lymph of the blood. Lymph is blood -without red particles; and blood, lymph with red particles. - -969. The chyle is transmitted into the lymph-vessels to mingle with the -lymph before it flows into the veins to mingle with the blood. - -970. The commingled fluids, chyle and lymph, pass into the blood very -slowly, drop by drop. The regulation of the rapidity of the admixture -seems to be the chief office of the valve placed at the termination of -the thoracic duct. When the operation is observed in a living animal, -it is seen that this valve prevents the new matter from flowing into -the blood in a full stream. If in a dog of ordinary size that has -recently eaten as much animal food as it chose, the thoracic duct be -opened in the neck, the dog being alive, there will flow from the duct -about half an ounce of fluid in five minutes (831); yet when this fluid -reaches the termination of the duct only a few inches further on, it -flows into the vein only drop by drop, at considerable intervals. One -great object of pouring the chyle and lymph into the venous system so -close to the heart (fig. CLXXVIII.), and of causing the commingled -fluid to pass under the action of that powerful engine before it is -transmitted to the lungs, seems to be, by the agitation to which it -is subjected in the right auricle and ventricle to accomplish the -most perfect admixture possible between the particles of the chyle -and lymph and the red particles of the venous blood; an object which -would be counteracted by the too rapid entrance into the current of the -circulation of the new and as yet imperfectly assimilated matter. - -971. After their due admixture by the powerful action of the engine -that works the circulation, the commingled fluids are transmitted by -the right heart to the lungs. There the watery portion of the chyle -and lymph is removed; the composition of the albumen and fibrin is -completed, these substances being changed from a weak and loose into -a strong and concentrated state; the solid particles are increased in -number, augmented in size, and changed from a white into a red colour; -carbon is given off; oxygen is absorbed; azote is alternately inhaled -and exhaled; and the ultimate result is, that the three fluids—chyle, -lymph, and venous blood—are converted into one homogeneous fluid, -arterial blood, the proper nutrient fluid. - -972. The particles of the chyle and lymph, on mingling with the blood, -are scattered through the mass, and become invisible, being apparently -lost among the innumerable red corpuscles; but it is not probable that -the chyle is immediately converted into blood. If the coagulation -of the blood be retarded by the addition of a small portion of the -carbonate of potass, the red particles gradually sink some lines -below the level of the fluid; and the supernatent liquid is whitish, -evidently from the chylous globules mingled with the blood. In ordinary -coagulation, the chyle globules are included among the immense number -of the red particles of the coagulum, and are thus indistinguishable; -but there is reason to believe that the chyle is not converted into -blood under at least from ten to twelve hours; it is certain, that in -that space of time after the completion of digestion, the serum of -the blood is frequently seen to be milk-white, from the quantity of -unassimilated chyle still contained in it. - -973. How the red colour of the blood is obtained, and whence the -capsules of the red particles are derived, if these bodies really -possess an external envelop, is wholly unknown. But it has been shown -(953 and 955) that in incubation the blood is formed from the substance -of the fluid yolk, without the action of any special organ; that at the -period when the blood is first generated, no such organs as appear to -influence the production of the blood in the adult are in existence; -it is, therefore, reasonable to infer that the formation of blood in -the adult may not be so dependent on the action of special organs as is -commonly supposed; and that the formation of blood from chyle, of blood -corpuscles from chyle corpuscles, may take place at all periods of life -under the influence of the same general vital conditions as it does in -the incubated egg. - -974. What change the matter of the blood undergoes by respiration, -whether it acquire something without which it is incapable of -maintaining life, or part with something the presence of which is -incompatible with life, is equally unknown. We only know that the -blood, during respiration, changes its colour; but of the nature of -the change produced upon its substance we are wholly ignorant. In the -present state of our knowledge, the ultimate fact is, that without the -change wrought upon the blood by respiration, the blood is incapable -of maintaining life; in fact, no proper nutrient fluid is formed. - -975. Once formed, the conservation of the proper proportions of the -composition of the blood is effected by the excretory processes -already described; by the removal of its superfluous water by the -lungs, skin, and kidneys; by the removal of its superfluous carbon, -azote, and oxygen by the lungs, liver, and kidneys; by the removal of -saline and mineral matters chiefly by the kidneys; and finally by the -instantaneous removal of products of decomposition formed in the course -of the organic actions, chiefly, it would appear, by the kidneys. - -976. Once formed, and duly concentrated and purified, the blood is sent -out by the left heart to the system. Driven by the heart through the -main trunks and branches of the aorta, the blood ultimately reaches the -capillary arteries, which do not divide and subdivide indefinitely, -but ultimately reach a point beyond which they no longer diminish in -size. Not all of the same magnitude, some are large enough to admit of -three or four of the red particles of the blood abreast; the diameter -of others is only sufficient to admit of two or even of one; others -are capable of transmitting only the clear and transparent liquor -sanguinis; while in many cases the membranous tunics of the capillaries -wholly disappear; the blood no longer flows in actual vessels, but is -contained in the substance of the tissues in channels which it forms -in them for itself (304). - -977. Under the microscope, says Müller, the blood corpuscles are -seen distinctly pouring from the smallest ramifying arteries into -vessels which grow no smaller. After leaving these, they again -assemble in the origins of veins formed in collected branches. The -blood corpuscles flow in the finest capillaries, one after another, -and often interruptedly. They are colourless when they flow singly; -accumulated more thickly, they appear yellow, and in still greater -quantity, yellowish red or red. In animals that have lost their -strength, the globules flow without stoppage: when the animal is weak -and the motion is retarded, the globules move by starts; they move -on, but go more rapidly by fits. In a still weaker animal they only -advance during the impulse of the heart, and then fall back a little. -When several arterial currents unite in an anastomosis, one current -always predominates and traverses the anastomosis alone, to mingle its -blood in the other currents. Thus the currents meet and divide in the -reticulate capillaries till all are collected again in veins. Sometimes -the direction of the current changes, when another current becomes -stronger, and the previous leader weaker, according to the pressure -exerted on the part. - -978. While the blood is thus traversing the capillaries, its colour -changes from a bright scarlet to a dark red. This change in the colour -of the blood is the certain sign that particles have been abstracted -from the circulating mass, and have been applied to the formation -and support of the fluid and solid parts through which the stream is -flowing. Some physiologists have satisfied themselves that they have -seen the actual escape of particles from the circulating current; that -they have witnessed the immediate combination of those particles with -the substance of the tissues, and even that they have beheld other -particles quitting the tissues and mingling with the flowing blood. -Other physiologists doubt whether the most patient observation, aided -by the most skilful management of the best glasses, can ever have -rendered such phenomena matters of sense. “I imagined,” says Müller, -“at an early period, that I had seen something like this in the setting -circulation; but by prolonging the observation I saw the globules move -on if the current continued.” - -979. But whether the human eye have ever actually seen or not an -interchange of particles between the blood and the tissues, it is -absolutely certain that such an interchange does take place. For,— - -1. Indubitable evidence has been stated (786, _et seq._) of continual -absorption from all parts of the body, yet there is no loss of -substance; there must therefore of necessity be a proportionate -deposition. - -2. Equal evidence has been adduced (688) that constant additions are -made to the blood through the organs of digestion, yet the quantity -of the blood in the body does not progressively and permanently -increase; it follows that a quantity must be abstracted from the blood -proportionate to the quantity added to it. - -3. The human germ, from a scarcely visible point, by the successive -additions of new matter progressively acquires the bulk of the adult -man. - -4. Organs whose special office it is to abstract particles from the -blood for the elaboration of specific secretions consist almost -entirely of congeries of blood-vessels. The agents are multiplied in -proportion to the extent of the labour assigned them. - -5. Growth, which is merely excess of deposition above absorption, is -active in proportion to the quantity of blood which circulates through -the growing part in a given time. The blood-vessels of a growing part -increase in number and augment in size is proportion to the rapidity of -the growth. In morbid growth, it is sometimes sufficient to stop the -process merely to tie the main trunks of the arteries distributed to -the part. - -980. By every organ and every tissue; by the membrane, the muscle, the -bone; by the brain, the heart, the liver, the lungs, particles are -abstracted from the countless streams that bathe them, or that flow -through them. In every case in which particles are thus abstracted by a -tissue the following phenomena take place:— - -1. Only those constituents of the blood are abstracted by the tissue -which are of the same chemical nature as its own. - -2. The constituents of the blood abstracted by a tissue, identical in -chemical composition with its own, are immediately incorporated into -its substance. - -3. The constituents of the blood abstracted by a tissue, as they are -incorporated into its substance, are not disposed fortuitously, but are -arranged according to the specific organization of the tissue, and thus -receive its own peculiar structure. - -4. The constituents of the blood which thus receive the peculiar -organization and structure of the tissue by which they are -appropriated, acquire all its peculiar vital endowments. - -981. It is manifest, then, that the tissues assimilate the blood just -as the digestive fluids assimilate the aliment. And this is nutrition, -the assimilation of the blood by the tissues and organs. Digestion is -the conversion of the food into blood; nutrition is the conversion of -blood into living fluids and solids. - -982. For the reasons assigned (757 and 758), it is probable that -the living fluids and solids, formed from the blood by the act of -nutrition, are not generated at the parts of the body where they -appear, but that, pre-existing in the blood, they are merely evolved -at those parts. Hence the variety and complexity of the processes for -the elaboration of the blood which have been described, and all of -which appear to be indispensable to bring the blood to a proper state -of purity and strength. The great effort of the system is put forth -in effecting the constitution of the blood. When the blood is once -formed, all the rest of the work appears to be easy; because, before it -reaches any part of the organization which it is destined to support, -the blood is already adapted, mechanically, chemically, and vitally, to -afford that support. Still since there are cases, as in the production -of gelatin, in which the substance does not appear to be pre-existent -in the blood, we are under the necessity of supposing that a material -change is effected in the constituents of the vital fluid at the time -and place of their escape from the circulation. - -983. How the constituents of the blood escape from the circulation and -incorporate themselves with the substance of the tissues there can -be no difficulty in conceiving, wherever the capillaries terminate -in membraneless canals, channels worked out for the reception of the -nutrient stream by the force of the current itself; and in every case -in which the capillaries, retaining their membranous tunics, remain -true and proper vessels, their contents escape through their delicate -walls by the process of endosmose (803), for which their structure -appears to be admirably adapted. - -984. But in the capillary vessels there exists only blood. Universally -and invariably before the blood passes from under the influence of the -capillary vessels it has ceased to be blood. Arterial blood is conveyed -by the carotid artery to the brain; but the cerebral arteries do not -deposit blood, but brain. Arterial blood is conveyed by the capillary -arteries to bone; but the osseous capillaries do not deposit blood, but -bone. Arterial blood is conveyed by the muscular arteries to muscle, -but the muscular capillaries do not deposit blood but muscle. The blood -conveyed by the capillaries of brain, bone, and muscle is the same; -all comes alike from the systemic heart, and is alike conveyed to all -tissues; yet in the one it becomes brain, in the other bone, and in the -third muscle. Out of one and the same fluid are manufactured cuticle, -and membrane, and muscle, and brain, and bone; the tears, the wax, the -fat, the saliva, the gastric juice, the milk, the bile, all the fluids, -and all the solids of the body (310). - -985. These phenomena are wholly inexplicable on any known mechanical -principles. It is equally impossible to refer them to mere chemical -agency, or to any properties of dead matter. We are therefore under -the necessity of referring them to a principle which, for the sake of -distinguishing it from anything mechanical or chemical, we term vital. -As the actions which take place between the integrant particles of -bodies, giving rise to chemical phenomena, are referred to one general -principle, termed chemical affinity, so the actions which take place in -living bodies, giving rise to vital phenomena, may be referred to one -general principal, termed vital affinity. The term explains nothing, -it is true, it merely expresses the general fact; but still it is -convenient to have a term for the expression of the fact. The property -itself will ever remain an ultimate fact in physiology, however exactly -the limits of its agency, and the laws according to which it modifies -the mechanical and chemical relations of the substances subjected to -its influence, may hereafter be ascertained; just as chemical affinity -will ever be an ultimate fact in physics, whatever discoveries may yet -be made of the extent of its agency and of the conditions on which its -action depends. - -986. It is then an ascertained fact, that there exists between the -blood and the tissues a mutual reaction, not of a physical, but of a -vital nature, in which the blood takes as active a part as the tissue, -and the tissue as the blood; the blood exerting a vital attraction on -the tissue, and the tissue on the blood. We only express this ultimate -fact when we say (and this is all we can do) that in every part of the -body, by virtue of a vital affinity, the tissue attracts from the blood -the molecules of matter appropriate to its chemical composition, and -the blood attracts from the tissue the particles which, having served -their purpose there, are destined to other uses in the economy; or, if -wholly useless, are absorbed into the current of the circulation to be -expelled from the system. - -987. We can see how the particles of matter which are attracted by the -tissue from the blood are so deposited and disposed that the tissue -always preserves its own shape, bulk, and relation to the surrounding -tissues. This definite arrangement is the result of an action which has -been already stated to be proper to the absorbent vessels. Previously -to the deposition of a new particle of matter by a capillary, an old -particle is removed by an absorbent, either a lymphatic or a vein. In -removing the old matter, the absorbent forms a mould into which the -capillary deposits the new molecules; and the form of every tissue and -organ depends on the kind of mould formed for the reception of its -nutrient matter by the absorbent vessel. The absorbents are thus the -architects of the system; and the capillaries are both chemists which -form the rough material employed in the structure, and masons which -deposit and arrange it. The conjoint action of both sets of vessels is -necessary to the formation of the simplest tissue; and it is by their -united labour that the compound organs are built up out of the simple -tissues. - -988. It is conjectured that the immediate living agents by which this -vital attraction is exerted between the blood and the tissues are -the organic nerves. These nerves consist of two sets, those which -enter as constituents into the tissues and those which accompany the -capillaries. It has been shown (304), that while the membranous tunics -of the capillaries diminish, the nervous filaments distributed to them -increase; that the smaller and thinner the capillaries the greater -the proportionate quantity of their nervous matter; and that this is -most remarkably the case in organs of the greatest irritability. It is -conceived that the capillaries, in consequence of the nervous structure -which thus envelops them, exert upon the fluid which is flowing through -them an influence perfectly analogous to that of the secreting organ, -in consequence of which similar particles are abstracted from the blood -as those which compose the tissue in which the operation takes place. - -989. It is further conjectured that the physical agent by which this -action upon the blood is effected is the galvanic fluid. Dutrochet -believes that he has actually formed muscular fibre from albumen by -galvanism. He considers the red particles of the blood as pairs of -electrical plates, and thinks that the nucleus is electronegative, -and the capsule electropositive. Müller has repeated and critically -examined the interesting experiments of Dutrochet; and while he arrives -in many essential points at different results, expresses the highest -admiration of the ingenious manner in which this philosopher has sought -to solve a great problem. “If,” says Müller, “a drop of an aqueous -solution of the yolk of egg (in which very small microscopic globules -are suspended) be galvanised, the currents discovered by Dutrochet will -be observed. The wave, proceeding from the copper or negative pole, in -which the alkali of the decomposed salt accumulates, is transparent, -from the solution of albumen by the alkali. The wave, proceeding from -the positive or zinc pole, particularly in its circumference, is -opaque, and white from the acid it contains. Both waves encounter, -and exactly in the line of contact a linear coagulum is immediately -produced, which assumes the form of the line of contact, and is curled -at times as the edges of the waves are meeting. The meeting of both -waves takes place with a lively motion, in the line of contact, when -the deposition of coagulum takes place; but as soon as the deposition -of coagulum has occurred, all is tranquil, and not the least trace of -motion is observed. It is therefore inconceivable how an observer of -the first rank, like Dutrochet, can pronounce this coagulated albumen -contractile muscular fibre, generated by galvanism; it is nothing but -coagulated albumen. This coagulum, besides, like the albumen which -is deposited by galvanism round the zinc pole, has no consistence, -but is composed of globules easily separated by stirring, and only -precipitated in the line where the two waves meet without cohesion.” - -990. But though science has not yet succeeded in ascertaining with -certainty the physical agency to which the ultimate changes that -take place in organized matter are to be referred, there cannot be -a question that they are dependent on physical agents; and the -legitimate object of scientific inquiry is to discover what those -agents are, and to ascertain the modifications they undergo by those -vital affinities to the influence of which they are subjected. - -991. The discoveries which science has already made relative to the -influence of certain physical agents on particular organs, and to the -influence of the whole circle of physical agents on the whole living -economy, have added not a little to human power over human health -and disease. But these agents also exert an influence scarcely less -momentous on the entire apparatus and action of the animal life, so -inseparably linked with the organic. An account will therefore be -next given of the structure and function of the nervous and muscular -systems. The exposition of these systems, which will be as brief as -possible, will be followed by a full account of the action of physical -agents on the whole of this complex and wonderful organization. The -detail of the ascertained phenomena will have a strict reference to -the development of the physical and mental powers of the human being, -and thereby a close and practical application will be attempted of -physiology to the production and preservation of health. - - -THE END. - - - - - -End of the Project Gutenberg EBook of The Philosophy of Health; Vol 2, by -Thomas Southwood-Smith - -*** END OF THIS PROJECT GUTENBERG EBOOK THE PHILOSOPHY OF HEALTH; VOL 2 *** - -***** This file should be named 60937-0.txt or 60937-0.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/6/0/9/3/60937/ - -Produced by Chris Curnow, Les Galloway and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the United -States without permission and without paying copyright -royalties. 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